[Objectives]To investigate the effects of losartan on cell apoptosis and the expression of caspase-3 and JNK proteins in kidney tissue in the adenine-induced renal fibrosis rats.[Methods]Thirty Wistar rats were randomly divided into three groups:control group(n=10),model group(n=10)and losartan group(n=10).The rats in the control group received saline,while those in the model group and losartan group both received adenine by gavage,for 21 d.After the renal interstitial fibrosis model was established,the rats in the losartan group were treated with losartan[10 mg/(kg·d)],while the rats in the control group and the model group rats were administered with the same amount of saline.The course of treatment was 30 d.Finally,the renal function,blood urea nitrogen(BUN),serum creatinine(Scr),creatinine clearance rate(Ccr)and the pathological morphology of the rats were detected.The apoptosis of renal tubular epithelial cells was tested by TUNEL.The caspase-3 and JNK protein expression was tested by Western blotting.[Results]After administering adenine for 21 d,the BUN,24 MTP and kidney/body weight in the model group were increased,significantly higher than the control group(P<0.01),and the Ccr was remarkably decreased(P<0.01),signifying that the renal interstitial fibrosis model was successfully built.After treating with losartan for 30 d,the Scr,BUN,and 24 MTP were significantly decreased(P<0.01),and the Ccr was significantly increased in the losartan group(P<0.01).In addition,in comparison to the model group,renal tubular epithelial apoptosis was decreased and caspase-3 and JNK expression was downregulated in the losartan group(P<0.05).[Conclusions]Losartan can reduce the adenine-induced elevation of Scr,BUN and 24 hMPT,increase Ccr,improve general condition of renal interstitial fibrosis in rats and ameliorate the progression of chronic kidney failure(CKD).The effectiveness of losartan is probably due to its ability to regulate caspase-3,JNK protein expression and attenuate renal cell apoptosis.