Pacific cupped oyster Magallana gigas (Thunberg, 1793) was introduced to Europe in the 1960s for aquaculture purposes. It was first described in the Adriatic Sea in the 1970s, in the Lim Bay, though this species has never been cultivated in Croatia. There are still very limited available information about this invasive species in the Adriatic. The aim of this thesis was to describe the reproductive cycle, size and structure of population of the Pacific cupped oyster in the Lim Bay. The research was carried out in the period from February 2017 to October 2018 during which the reproductive cycle of the Pacific cupped oyster was followed through the histological analysis of the gonadal tissue. Furthermore, on four locations along the Lim Bay analysis of the size of the length structure of this species was conducted. The results showed that the conditions in the Lim Bay are suitable for reproduction of this type of M. gigas and that it spawns mainly in the summer period. Male and female oysters had a synchronous reproductive cycle with minor differences in the process of gametogenesis. Population of this oyster species in the Lim Channel was very high and ranged from 33 to 248 individuals/m2. The range in size varied from 21 to 89 mm. The given data represents the first quantiative figures for this species in the Adriatic Sea and prove, together with the reproductive cycle results, that the Pacific cupped oyster in the Lim Bay has developed self-sustaining wild populations.