Rumen is a complex ecosystem where feed consumed by animals is digested by the help of rumen protozoa. They plays an important role in contributing nutrients to the host animal. This study aimed to investigate the effects of dietary inclusion of unicellular microalgae Chlorella vulgaris spp. on total count and generic composition of protozoa in cows rumen. In this study, dietary treatments were tested during three 21-d experimental periods. Each of period content different amount of microalgae supplement. In the first experimental period in cows feed was added 30g (3,14g/kg of DM) of Chlorella, in second period-90g (9,6g/kg of DM) of Chlorella and in third period-170g (18,7 g/kg of DM). As a result of this study, ciliates of 10 genera were detected and identified. The number of this genera and total amount of ciliates were counted. The analysis of rumen protozoa population in tested cows shows visible effect of the presence of microalgae in cows dietary. In particular, the density of ciliates protozoa of the cows treated with 90 and 170 g of algal supplement was visibly higher compare to results from the control diet. Microalgae-based supplement diet had stimulative effect on ruminal protozoa population and caused increasing of many protozoa genera such as Isotricha, Dasytricha, Charonina, Buetschlia, Ostracodinium, Ophryoscolex.