Abstract: Objective: The current study was conducted to investigate the effect of dietary inclusion of 5% Guar Meal (GM) as a partial replacement for soybean meal (SBM) with or without β-mannanase enzyme (0.03%) on performance, carcass traits, blood biochemical and histological picture of intestine as well as immunity parameters of broilers. Materials and Methods: In this study, about 496 one-day-old male broiler chicks (Ross 308) were divided to 4 groups with 4 replicates of 31 chicks each. The trial continued for 35 days. The data were analyzed as 2×2 factorial arrangement in a completely randomized design. Results: The results showed that body weight gain (BWG), dressed weight (DW), thigh weight and breast weight were significantly lowered in birds fed diet containing 5% GM than those fed SBM diet (p<0.05). Villus height were significantly (p<0.05) reduced in birds fed diet containing 5% GM compared with those fed SBM. β-mannanase supplementation of GM diet significantly improved BWG, DW, breast weight, thigh weight, feed conversion ratio (FCR), villus height and increased thymus and bursa lymphocyte number (p<0.05). Conclusion: The results demonstrated that GM could be used at 5% of broiler diet with β-mannanase supplementation without adverse effects on growth performance and blood biochemistry.