In spite of microalgae importance in the fatty acids field, there has been no review of the lipid composition of native Uruguay flora. The objective of this work is to compare the composition of the Chlorella vulgaris biomass collected at a sewage treatment pool with the biomass of laboratory cultures prepared from a starter of the first. Adaptation possibilities and biomass modification were thus determined to find an application field for wasted natural resource. Laboratory cultures were carried out under different lighting (continuous and 16:8 photoperiod), and with different nitrogen sources (NH4Cl, KNO3, and urea) at different concentrations. The results showed that, in order to favour the polyunsaturated acids content, nitrogen should be supplied in a molecular form of difficult assimilation (urea), and with discontinuous lighting. As a general conclusion,it can be said that in the case of Chlorella vulgaris isolated in Uruguay, the lipid content of the biomass and its fatty acid composition depend on culture conditions and the stage of development. Particularly, samples collected in natura do not show the same values aas the cultured in vitro. So it is possible to modify the conditions to achieve variations that may increase productivity of special fatty acids.