The island of Ugljan area is famous for its millenia-old olive growing and processing. Since ancient times the quality of olive oils from the island has been well-known. Even today there are about 300 000 olive trees on the island. There are autochthonous varieties on the island, which are not determined and morphologically described in detail, so the aim of this paper is to research the characteristic of morphological sterility in five indigenous island varieties: karbunčela, puljka, puljižica, oštrica and drobnica. In spite of millenia-old tradition of olive growing, the characteristic of morphological sterility as a phenomenon started to be researched only in 20th century. Namely, research has shown that the percentage of wilted and fallen flowers during the blooming period has a direct impact on the number of fruits that will reach harvest time. Research done and described in this paper was carried out at two intervals owing to the fact that some varieties bloom earlier and some later. On 18th and 19th May samples were taken for analysis of varieties karbunčela, puljka and drobnica and on 29th May samples were taken for varieties oštrica and puljižica. The samples were taken from four trees of each variety on different sites of the island, namely 25 flowers from each tree, from the southern circumferential part of the tree. So we had a hundred samples from each variety in order to get more relevant data. Next, the length of blooming was measured, the precentage of functionally male flowers was determined and consequently morphological sterility for each variety was established. The results have shown that there are significant differences in the percentage of male flowers between different varieties. Karbunčela variety had a little less than 20% of male flowers, varieties puljka and puljižica had about one third of functionally male flowers. Oštrica variety had a little less than a half functionally male flowers, while drobnica variety, which is used as a pollinator, had 75% of functionally male flowers.