Background/Aim: Investigators have reported that the nonmuscle myosin heavy chain B (SMemb) expression is enhanced in various types of glomerular diseases which develop into nephrosclerosis. In renal transplantation, transplant glomerulitis is often recognized during acute rejection. Therefore, we hypothesized that SMemb plays important roles in acute kidney rejection. To evaluate the role of SMemb in the development of kidney rejection, we examined its expression in rat kidney transplantation models. Methods: We used Lewis rats as recipients and Wistar rats as donors. Group I: controls; group II: isograft model; group III: allograft model; group IV: as group III +10 mg/kg/day of ciclosporin A (CsA), and group V: as group III + CsA administration for 5 days postoperatively. Histopathological and SMemb immunohistochemical studies were completed. Results: Clear enhancement of SMemb expression was found on day 3 in group III. In groups I, II, IV, and V, SMemb was faintly expressed in the glomerular cells. However, after termination of CsA treatment, the SMemb expression increased. The expression of SMemb was higher in the allograft model than in either isograft or CsA-treated models. Conclusions: Immunohistological investigations show that the SMemb expression was significant from an early stage at which histopathological reactions were hardly identifiable. This, therefore, could be useful for an earlier diagnosis of acute rejection.