The aim of this study was to determine the effect of rapamycin on renal ischemia-reperfusion injury (IRI) in mice. Renal IRI was induced in male BALB/c mice by clamping both renal pedicles for 45 min. The mice were treated with either vehicle or rapamycin (2 mg/kg/day) by oral gavage, starting 1 day before the IRI and continued daily till killing. The mice were killed on days 1, 3 and 7 after the operation. The severity of the renal IRI was assessed by serum creatinine levels and renal histology. Proliferation of renal tubular cells was quantified by immunohistochemical staining for proliferating cell nuclear antigen (PCNA). One day after the IRI, the serum creatinine levels of rapamycin-treated mice were significantly higher than those of the vehicle-treated mice. Kidney sections from rapamycin-treated mice showed more marked tubular damage and significantly lower number of PCNA-positive cells. The number of PCNA-positive cells in the rapamycin-treated mice remained significantly lower on day 3 after the IRI. By day 7 after the IRI, the serum creatinine levels, renal histology and positive PCNA staining in the kidney sections became similar between the two treatment groups. We conclude that in this murine model of renal IRI, rapamycin treatment aggravates renal IRI during the first 3 days after the insult. This effect might be mediated, at least partly, through inhibition of renal tubular cell proliferation.