This study has been conducted to evaluate the effects of certain media containing various protein sources on the in vitro maturation (IVM) of cat oocytes. In this study 1013 oocytes obtained from 40 cats underwent ovario-hysterectomy surgeries for the purposes of spaying were used. Ovaries were brought to the laboratory in Dulbecco's PBS at 25-30 degrees C. The recovered oocytes were left to mature for 48 hours in Ham's F-10 media supplemented with different protein sources. In this study four experimental groups were designed: Group I: Fetal Calf Serum (FCS), Group II: Bovine Serum Albumin (BSA), Group III: Estrus Cat Serum (OCS), Group IV: Control (No protein supplementation). The incubator conditions were 38.5 degrees C temperature, almost 100% humidity and a gaseous mixture (5% O2, 5% CO2, 90% N2). At the end of the maturation period, the oocytes were fixed and stained. The maturation rates were determined under 400 x magnification on a phase-contrast microscope. Metaphase II (M II) rates were 6.2% (14/255), 16.5% (43/260), 13.1% (36/273) and 13.3% (30/225) in Groups I, II, III and IV, respectively. The maturation rate in the Group I where FCS was used as protein additive was significantly lower (P<0.001) than other groups. The ratio of oocytes reaching M I+M II stages was 28.6% (73/255), 40.3% (105/260), 31.1% (85/273) and 30.2% (68/225), respectively. The difference in the Group II (BSA added), was significantly superior to the other groups (P<0.05). In conclusion, although homologous protein source OCS was ineffective and FCS has negative effects, it was determined that using BSA as the protein additive for the medium will be beneficial for in vitro maturation of cat oocytes.