Here, we investigated the effect of l-ascorbic acid (AA) supplementation on the CYP2E1 expression level and oxidative stress in various tissues such as the liver, kidney, pancreas, and brain of streptozotocin (STZ)-induced diabetic rats. An increased cytochrome P450 2E1 (CYP2E1) expression level with a concomitant increase in the production of reactive oxygen species were found in all the tissues of STZ-induced diabetic rats tested compared with an untreated control, suggesting the possible diabetes-induced tissue injury. In contrast, the AA supplementation to the diabetic rats alleviated these experimental parameters in a tissue-specific manner. AA affected the liver most severely followed by the kidney. There was little or no effect of AA supplementation on the brain and pancreas. The circulation level of the ketone bodies, inducers of CYP2E1, was also decreased by AA supplementation compared with those of the diabetic rats. Therefore, the suppression of ketone production by AA can be one of the mechanisms of a reduction in CYP2E1. These results suggest that AA plays an important role in reducing elevated CYP2E1 expression level and the oxidative stress mediated by type 1 diabetes with a tissue-specific variation.