Abstract: The aim of this study was to investigate the effect of L. bulgaricus and S. thermophilus genera on serum cholesterol and triglyceride lowering potential of probiotic in guinea pigs and the changing pattern of above serum parameters after termination of the treatment. The effects of oral supplementation of probiotics to animals have been carried out in many occasions but their outcome after the termination of treatment is lacking. Twenty four eight weeks old guinea pigs were selected randomly divided into two groups (n=12) ) the test and the control, were reared in six cages (four per cage). Both groups received control mash diet (based on corn and soybean) during the experiment, to meet the nutrient requirements. A 5 ml of aqueous medium culture of L. bulgaricus and S. thermophilus with 1.76 x 109 and 1.5 x 108 colony forming units/ml, respectively were given to test animals for fourteen days and the control animals were given the same volume of distilled water. Blood samples were withdrawn by heart puncture at 14 and 21 days after the initiation of probiotic supplementation and serum total cholesterol, triglycerides, HDL cholesterol and total protein levels were assayed in both groups. The total cholesterol level of the test group was significantly lower (p<0.01) than the control group after 2 weeks and it increased slightly after the termination of probiotic supplementation. HDL cholesterol level was significantly higher in test animals after 3 weeks (p<0.05). There were no significant differences (p>0.05) in serum triglycerides, total protein, weight gain, body temperature, food and water intakes and body temperature between the control and treated groups. It was concluded that live probiotics significantly reduced the serum total cholesterol during the treatment period and increased the HDL cholesterol significantly following termination of the treatment. It is suggested that the feeding of probiotic does not affect food intake and bring up