Alpha-amanitin (alpha-AMA), the primary toxin of Amanita phalloides, is known to cause nephrotoxicity and hepatotoxicity. Resveratrol is an antioxidant that has shown efficacy in many nephrotoxicity models. The aim of this study was to investigate the effects of resveratrol against the early and late stages of alpha-AMA-induced nephrotoxicity, compared to those of silibinin, a well-known antidote for poisoning by alpha-AMA-containing mushrooms. Mice kidney tissues were obtained from five groups: (1) alpha-AMA + NS (simultaneous administration of alpha-AMA and normal saline), (2) alpha-AMA + SR (simultaneous administration of alpha-AMA and resveratrol), (3) alpha-AMA + 12R (resveratrol administration 12 h after alpha-AMA administration), (4) alpha-AMA + 24R (resveratrol administration 24 h after alpha-AMA administration), and (5) alpha-AMA + Sil (simultaneous administration of alpha-AMA and silibinin). Histomorphological and biochemical analyses were performed to evaluate kidney damage and oxidant-antioxidant status in the kidney. Scores of renal histomorphological damage decreased significantly in the early resveratrol treatment groups (alpha-AMA + SR and alpha-AMA + 12R), compared to those in the alpha-AMA + NS group (p < 0.05). Catalase levels increased significantly in the alpha-AMA + SR group, compared to those in the alpha-AMA + NS group (p < 0.001). Early resveratrol administration within 12 h after alpha-AMA ingestion may reverse the effects of alpha-AMA-induced nephrotoxicity, partly through its antioxidant action, thereby suggesting its potential as a treatment for poisoning by alpha-AMA-containing mushrooms.