This study investigates whether the toxicity in kidneys as well as oxidative stress varied according to the dosing time of an immunosuppressive agent “mycophenolate mofetil (MMF)“ in Wistar Rat. 300mg/kg of MMF was injected by intraperitonal at four different circadian stages (1, 7, 13 and 19h after light onset, HALO). Rats were sacrificed after 3days, and the kidneys were removed for determination of oxidative stress and histological analysis. Biochemical variable (creatinine, urea) was performed. Statistical analysis showed that MMF administration at 7 HALO produced a renal toxicity assessed by the significant increase in both blood creatinine and urea and antioxidant activity assessed by malondialdehyde and protein carbonyl levels indicating an induction of lipid peroxidation in oxidative damage. Whereas, at this time MMF induced a decrease the enzyme activities of renal catalase and superoxide dismutase, with a renal histopathology alterations (glomerular atrophy and lesions within proximal tubules). However, when MMF was injected in the middle of the dark-activity phase it produced a very mild renal toxicity and low oxidative stress. The obtained data indicate that the maximum of renal toxicity is observed when MMF was injected in the middle of the light- rest span in rats.