Modality (lat. modus) is a lingustic term that is used to express the illocutionary act which usually refers to the subject's attitude towards the statement. Modality was the topic of many different researches, in spoken and in sign languages. The aim of this research was to describe five modal categories (epistemic, alethic, deontic, volition and root modality) in Croatian Sign Language (HZJ). In this research, video data, that was priorly filmed and collected for the purpose of comparison of HZJ, American Sign Language (ASL) and German Sign Language (DGS), was anaylized. The anaylisis confirmed that for HZJ epistemic and alethic modality are expressed by way of layering strategy, i.e. by simultaneous production of manual signs along with nonmanual markers. Deontic modality, volition and root modality in HZJ are expressed by way of manual modal verbs concatenation. This paper contributes to the description of HZJ grammar, which is complex and independent of the Croatian language grammar. Apart from the linguistic contributon, this research can find its applicaiton in upbringing, education and rehabilitation of deaf childredn as well as in teaching HZJ as a second lanuage.