Abstract: Objective To investigate the effects of losartan on activation of signal transducers and activators of transcription of STAT3 and mRNA expression of STAT3 in glomeruli of diabetic rats. Methods STZ-induced Wistar diabetic rats were randomly divided into two groups: untreated diabetes group, treated group by losartan 40 mg/kg in addition to normal control group. The renal cortical tissues were obtained and used to isolate glomeruli. The protein expression of p-STAT3 in glomeruli was observed by immunohistochemistry and Western blot. The protein expression and (mRNA) of STAT3 were observed by Western blot and RT-PCR separately. Results The expressions of STAT3, p-STAT3 and STAT3 mRNA were significantly increased in the diabetic glomeruli without losartan treatment vs diabetic group(P<0.01). The expression of p-STAT3 was decreased in losartan group vs control (P<0.05). However, losartan had no effect on the expression of STAT3 and STAT3 mRNA. Conclusion STAT3 signal pathway may be involved in diabetic nephropathy. (Regulation) of phosphorylation of STAT3 may be responsible for the renal protective effects of losartan in diabetic rats.