Four Ostracoda species belonging to one family, Halocyprididae, were found in plankton material collected from the Scotia Sea and off the King George Island (the Antarctic) during the austral summer 1988/1989. Alacia belgicae, A. hettacra and Metaconchoecia isocheira were dominant making up to nearly 99% of all Ostracoda. The horizontal distribution was modified by variability of hydrological conditions. The higher concentrations of chlorophyll a and phytoplankton, which were found in the mid- and eastern parts of the Scotia Sea, coincided with the highest densities of Ostracoda. The influence of ice pack presence in the Scotia Sea upon the higher abundance of Ostracoda in the period investigated in comparison with the earlier studies was distinctive. A vertical distribution analysis confirmed that the three above-mentioned endemic species were most abundant in the mesopelagial. The population structures of A. belgicae, A. hettacra, and M. isocheira were analysed. The presence of the youngest stage of A. belgicae in the Scotia Sea confirmed the beginning of reproduction of this species at that time. The vertical distribution patterns of A. hettacra and M. isocheira populations were similar, although their age structures in comparison with A. belgicae differ significantly. This was consistent with their higher mean population stage values.