This thesis deals with research and comparison of the idioms of biblical origin in the Italian and Croatian language. Since the biblical origin idioms belong to internationalisms, i.e. interphraseologisms, they represent an important group within the phraseology of each language. As they originate from the same source, i.e. from the Bible or the Holy Scripture, their analysis at interlingual level enables a better comprehension of their in-depth structure. Italian and Croatian are not genetically related languages, the Croatian language belongs to Slavia Romana (Slavia Latina), though, and for this as well as for other reasons there is a discernable influence of Latin on Italian and Croatian phraseology, respectively. However, different reception of the biblical origin idioms has been perceived in these two languages. The theoretical framework of this thesis is a comparative phraseology. For this purpose phraseologically contrastive papers in the Croatian, German, Italian and Spanish language in general, and contrastive papers on the biblical origin idioms, in particular, were collected and studied. The corpus of this research are the idioms of biblical origin that we obtained by excerpting examples from Italian and Croatian phraseological dictionaries (monolingual, bilingual, printed and online). Methodology consisted of a contrastive analysis of excerpted idioms, where we mostly focused at the synchronic level bearing in mind that in each comparative analysis there is a diachronic aspect within sociocultural framework as well as an intercultural comparison. As the idioms are linguistic units established mainly secondarily, contrastive analysis uses particularly induction to describe these units derived from the units of the primary systems (vocabulary, syntax and morphology), and therefore it is always necessary to analyze the lexical, structural-syntactic and structural-semantic aspects. We also used a quantitative approach as much as possible and relevant in this study. The aim of this contrastive analysis has been mainly to determine phraseological equivalents in both languages. We divided the equivalence into full, partial, purely semantic and zero, and possible idiomatic false friends were taken in consideration within this subsystem. This synchronous contrastive analysis of the idioms of biblical origin in the Italian and Croatian language indicates similarities and differences at the structural, syntactic and semantic levels, and their equivalence at interlingual level. This thesis represents the attempt to fill the gap in contrastive analysis of the idioms of biblical origin in the Italian and Croatian language and thus contribute to the development of comparative phraseology in general as well as to the research of the biblical origin idioms that have a strong influence in these two languages, both in the past and today, not only in standard language and in regional versions, but also in regional and local dialects. The corpus of biblical idioms in Italian contains 209 examples, and 170 in Croatian, respectively. Contrastive analysis was approached from different points of view, using the methods of the Zagreb phraseological school and methods of phraseologists who write in German, as well. A relatively large number of idioms with full equivalence (80 examples) indicates most probably a strong influence of the same source, Latin translation of the Bible, i.e. Vulgata in both languages, as well as their belonging to the same religious denomination and ritual group, while does not confirm the results of numerous contrastive analyses of other microsystems in languages. The number of examples of partial equivalence, 45 in both corpora, differs from much contrastive analysis of phraseological microsystems of two or more languages. Equivalent idioms often exceed the number of congruent ones, but in regard to the aforementioned reasons such a distribution is not particularly surprising. There is only one example of purely semantic equivalence in which significant lexical and semantic differences are discernible, while the picture itself is different. Furthermore, both languages also have a significant number of idioms that have no equivalent in (that) other language, respectively: 83 idioms in Italian and 44 in Croatian. This indicates the cultural-semantic discrepancy in these two languages, different influences in the phraseological treasure, and the vitality of both languages, as well. In this way the power of the phraseology of small nations has been revealed, even in terms of the idioms that traditionally belong to internationalisms. Strong influence and privileged place of Latin in the liturgy as well as in the culture and public life of both nations, had left the traces in phraseological treasure of both Italian and Croatian – in each of them in a special way – and marked other phraseological microsystems, in particular the idioms of biblical origin. And biblical origin idioms, whose stylistic values does not differ significantly, still today have a strong influence on the Croatian literary and spoken language, in its standard version, in all substandard varieties, as well, and significantly contribute to the peculiarity of the Croatian language, particularly from the point of view of speaker identification criteria. While this is not the case in Italian where there is a completely different dynamics in relation to other Romance languages. Perhaps only diachronic and areal phraseological research will shed some light on this richness and peculiarity of Croatian and its millennial tradition of using the idioms and paremias of biblical origin. This comparative analysis also shows all the complexity of the idioms regarding both expression and content, and their particularity. Certainly, we do not avoid reflecting on the need of structural language analysis at three abstract levels, i.e. the need for triple articulation in order to understand more seriously and explore more thoroughly the phraseology of European languages, but also to approach analytically more strictly to a more pronounced interest in the words connections that have been perceived in linguistics in recent decades.