This study was conducted to investigate the effects of pennyroyal (Mentha pulegium L.) extract on carcass yield and serum cholesterol in broiler chickens. A total of 320 one-day old broilers (Ross 308) were randomly allocated to 4 treatments, 4 replicates with 20 birds in each in a completely randomized design. Treatments included were control and addition of various levels of pennyroyal extracts at 50, 100, and 150 ppm in diets. The results showed that inclusion of 150 ppm pennyroyal extract in diets increased live body weight, carcass relative weight, carcass efficiency and heart relative weight (P<0.05). In addition, inclusion of pennyroyal extract at levels of 100 or 150 ppm in diets increased relative weights of breast and wings (P<0.05). Furthermore, the lowest serum cholesterol and triglyceride and low density lipoprotein levels were obtained in birds fed 150 ppm pennyroyal group (P<0.05). The results of present study showed that pennyroyal (150 ppm) improved carcasses yield and serum cholesterol.