This study evaluates the effects of different levels of guanidinoacetic acid (GAA) supplement on growth performance and gut morphology in broilers (Ross 308 strain) raised at high altitude (2100 m). A total of 300 one-day-old male broiler chicks (Ross 308 strain) were used in a completely randomized design with five treatments and four replicate pens of 15 birds in each.Five dietary treatments were prepared by supplementing GAA at 0 (control), 0.5, 1.0, 1.5, and 2.0 g/kg to corn-soy based diet and fed to broilers from 1 to 42 days of age. Results indicated that weight gain and feed: gain ratio was significantly improved in the chickens when GAA was supplemented to control diet. Carcass and breast yields were significantly increased by GAA supplementation at 1 g/kg relative to the control. On the other hand, dietary inclusion of GAA significantly (P<0.05) reduced the proportions of liver, heart and abdominal fat when compared to the control. The villus height, width and absorptive surface area in duodenum, jejunum, and ileum sections were significantly improved at GAA supplementation above 0.5 g/kg. However, the crypt depth showed a significant decrease in all parts of the small intestine compared to the control (P<0.05). In conclusion, supplementing broiler diets with GAA could be an effective strategy to improve growth performance and gut function.