Objective: Study the effects of adding three commercial probiotics to broiler chicks' ration on performance.Design: Randomized completely design.Animals: Seven hundred and twenty day-old male Ross 208 broiler chicks.Procedure: The chicks were randomly assigned to four dietary treatments so that each treatment contained six replicate floor pens of 30 chicks. One treatment (as control) received a basal corn-soybean meal diet without any antibiotics, growth promoters, coccidiostates. Three other treatments fed diets including commercial probiotics A, B, or C respectively. Body weight (BW), food consumption (FC), feed conversion ratio (FCR) and mortality were evaluated at 21, 42, and 49 days of age.Statistical analysis: Data for all response variables were subjected to ANOVA. Variable means for treatments showing significant differences in the ANOVA were compared using the Tukey's test.Results: By the end of 21-days old of age, feeding diets supplemented with probiotics A and C increased BW significantly (P < 0.05), in comparison with control, while supplementation diet with probiotic B had no significant effect on BW. At the end of experimental period, dietary treatments did not affect BW significantly. However, adding commercial probiotics to basal diets caused partial increasing in BW. Supplementation diets with commercial probiotics decreased FCR significantly (P<0.05) by the end of 21-days old of age. Although no significant differences were observed among FCR in dietary treatments, at the end of experimental period, but chicks fed diets containing probiotics A and B, had better FCR when compared with control.Conclusion: According to the obtained results, it seems that supplementation of broiler chicks' rations with commercial probiotics which were used in this feeding trial could improve broiler performance, especially in the first three weeks of rearing period.