In living organisms, oxidant and antioxidant systems are in a balance. In the current study, we aimed to study the effects of Cryptococcus humicola, which is food based yeast whose cholesterol lowering activity is under investigation, on oxidant and antioxidant systems. 31 adult male, Wistar albino rats weighing 200-250 gr were included in the study. Rats were divided into four groups based on their diets. Rats in Group 1 (Control Group) was fed control diet, Groups 2, 3 and 4 were fed high cholesterol, high cholesterol plus low dose yeast diet (0.1% lyophilysed yeast) and high cholesterol plus high dose yeast diet (2% lyophilized yeast), respectively. After fifty six days, serum samples were obtained from blood of all rats. Total antioxidant capacity (TAS), total oxidant capacity (TOS) and oxidative stress index (OSI) values were determined in the serum samples. Within the four groups there were no statistical changes on the TAS, TOS and OSI values in the four the groups. In conclusion, this may lead to questioning the efficiency of the diet. It may be possible to show the antioxidant activity of Cryptococcus humicola by increasing the yeast dose, number of subjects and duration of the experiment.