Анотация: The objective of this study was an evaluation of the effects of different growth promoters: probiotic Lacto-Saccо (Alltech, Inc. USA), nutritive premix Pharmastim and nutritive antibiotic Avilamycin on the cecal microflora and performance of broiler chickens. The experiment was conducted using four feeding groups of one-d-old broiler chicken: Group I: Basal diet without supplement (Untreated control); Groups II, III and IV: Basal diet supplemented with probiotic Lacto-Saccо, (1.0 kg/t); nutritive premix Pharmastim, (0.3 kg/t); and nutritive antibiotic Avilamycin (5,0 mg/kg), respectively. The addition of Lacto-Saccо to the basal diet significantly increased the count of lactobacilli and enterococci in the cecum of the broiler chickens and depressed the count of coliforms by the low pH of cecal content. There was no significant difference in the count of lactobacilli, enterococci, and coliforms present in the cecum of the untreated control, Pharmastim and Avilamycin-fed groups. Lacto-Saccо enhanced growth of beneficial microorganisms, regulated the microbial environment in the cecum. Lacto-Saccо significantly increased the body weight of broiler chickens (P<0.001), compared to the untreated control and the groups fed Pharmastim and Avilamycin. The Lacto-Saccо, Pharmastim and Avilamycin supplements improved feed conversion ratio by 8.8,1.1 and 1.9 (P<0.001), compared to the untreated control, respectively.. - These results suggested that feed additives based on microorganisms provide an alternative to antimicrobial substances in broiler nutrition. Probiotics, and especially Lacto-Saccо can reduce or replace antibiotics used for growth promotion in broiler chickens