Objective:To evaluate the effect of losartan on acute kidney injury (AKI) and the relationship with mitochondrial fusion-fission in septic mice.Methods:One hundred and twenty-eight SPF male C57BL/6J mice, aged 6-8 weeks, weighing 20-25 g, were divided into 4 groups ( n=32 each) using a random number table method: sham operation group (Sham group), sham operation+ losartan group (Sham+ LOS group), sepsis-associated AKI group (SA-AKI group), and sepsis-associated AKI+ losartan group (SA-AKI+ LOS group). Sepsis was induced by cecal ligation and puncture in anesthetized mice. Sham+ LOS group and SA-AKI+ LOS group received intraperitoneal injection of losartan 5 mg/kg, once a day, for 3 consecutive days, starting from 3 days before sham operation or developing the model. The equal volume of solvent was given instead in Sham group and SA-AKI group. Twenty mice were randomly selected to observe the survival 7 days after surgery. At 24 h after sham operation or establishing the model, serum blood urea nitrogen (BUN) and creatinine (Cr) concentrations were determined by the colorimetric method, and serum concentrations of tumor necrosis factor-alpha (TNF-α), interleukin-6 (IL-6) and high-mobility group box 1 protein (HMGB1) were measured using enzyme-linked immunosorbent assay. Renal tissues were obtained for microscopic examination of pathological changes which were scored and for determination of mitochondrial membrane potential (using JC-1 method) and expression of dynamin-related protein 1 (Drp1) and mitofusin-2 (Mfn2) (using Western blot). Results:Compared with Sham group, the survival rate was significantly decreased, the serum BUN, Cr, TNF-α, IL-6 and HMGB1 concentrations and renal tubular injury score were increased, the ATP content and MMP were decreased, the expression of Drp1 was up-regulated, the expression of Mfn2 was down-regulated ( P<0.05), and pathological changes were found in renal tissues in SA-AKI group and SA-AKI+ LOS group. Compared with SA-AKI group, the survival rate was significantly increased, serum concentrations of BUN, Cr, TNF-α, IL-6 and HMGB1 and renal tubular injury score were decreased, the ATP content and MMP were increased, the expression of Drp1 was down-regulated, the expression of Mfn2 was up-regulated ( P<0.05), and the pathological changes of renal tissues were significantly attenuated in SA-AKI+ LOS group. Conclusions:Losartan can alleviate AKI in septic mice, and the mechanism may be related to promoting mitochondrial fusion and inhibiting mitochondrial fission.