The antibacterial effect of Thyme species was relatively approved but the effect of this plant on bacterial population of intestine in chickens and consequently on bacterial load of chicken meat following administration of thyme was not investigated. For evaluation of thyme effect on growth indices, microbial contamination of meat and microbial population of cecal content, 180 broiler chicks were divided into 4 equal groups with 3 replicates and were reared until 42 days. Chickens in different groups were treated with different doses of thyme (0, 0.25, 0.50 and 1 percent) in diets. The weight gain, feed consumption and feed conversion rate were calculated weekly. In the end of 42 days old, all chickens were slaughtered. The population of Escherichia coli per gram of cecal contents and contamination of meat with Escherichia coli were assayed. The data showed that supplement of 0. 5 and 1 percent of thyme to diet elevated weight gain and decreased feed conversion rate. Furthermore, addition of 0.5 and 1 percent of thyme to diet can decrease microbial population of cecal content and meat. In conclusion, the addition of thyme to diet may improve growth rate and hygienic parameters in chicken meat