OBJECTIVE To explore the effect of dibutyl phthalate (DBP) on the biochemical enzymes and lipid peroxidation in rats. METHODS Healthy 6-week old male Sprague-Dawley rats were randomly divided into 4 groups with 16 in each. DBP dissolved in peanut oil was administered by gavage at dosages of 0, 250, 500 and 1000 mg/(kg x d). After 2- and 4-week DBP exposure, 8 rats in each group were killed, with certain organs selected and weighed. The activities of biochemical enzymes and glutathione peroxidase (GSH-Px) and the levels of glutathione (GSH) in the serum and testis homogenate were determined respectively. RESULTS DBP induced a rise in the liver organ body weight ratio, but a fall in the testis organ body weight ratio, and it was significant in the highest exposure group compared with the control after either 2-week or 4-week treatment (P < 0.01). After 2-week DBP exposure, GSHPx activities in the serum and GSH levels in the testis homogenate showed a decreasing tendency, but GSHPx activities increased markedly in the testis homogenate (P < 0.05). After 4-week DBP exposure, while alkaline phosphatase (ALP) activities in the serum revealed an increasing tendency, sorbitol dehydrogenase (SDH) activities were inhibited significantly in both the serum and the testis homogenate at the dosage of 1000 mg/(kg x d) compared with the control group (P < 0.01). Furthermore, GSH contents in the serum were also affected at this dose (P < 0.05). CONCLUSION The results indicate that DBP administration strongly affects the liver and the testis organ body weight ratios. Lipid peroxidation is one possible toxic mechanism caused by DBP. SDH may be one of the most sensitive toxic indices when exposed to DBP.