Abstract: Objective:To investigate the effect of different microbial environment（open system and barrier system） on some biologic characteristics of Wistar rats.Methods: 40 SPF Wistar rats were assigned into two groups respectively.Group 1 was housed in barrier system,while group 2 was kept in open system.The body weight of rats were measured weekly.After having been kept in the experimental environment for 35 days,14 hematology and 15 serum chemistry parameters were analyzed and 9 organ weights were measured in rats.Results: Rats housed in barrier systems grew faster than that in open systems（P＜0.05）.The values of RBC,WBC,PCT,PLT,GOT,GGT,GPT,CK,TB of rats kept in barrier system were lower than that in open system（P＜0.05）,while the values of CHO,LDL-C,HDL-C of rats in barrier system were higher than that in open system（P＜0.05）.There was no significant difference of relative organ weights between the two groups.Conclusion: There are some differences of biological characteristics of animals kept in barrier system and open system.