Bombyx mori L. larvae exposed to 4-n-nonylphenol (4-NP; 0.05, 0.1, 0.2, and 0.4 g per kg of nutrient) in the laboratory were studied with respect to superoxide dismutase, catalase, and corresponding mRNA levels in gonads during different developmental stages (larval, pupal, and adult). In addition, malondialdehyde contents were measured. An increase in malondialdehyde content was observed at the larval, pupal, and adult stages. In addition, an increase or decrease in superoxide dismutase, catalase, and the gene transcript level of superoxide dismutase and catalase was detected at the different stages. The changing trend in mRNA levels of these enzymes was not always consistent with that of enzyme activity. These results suggest a relationship between 4-NP and alterations in the levels of antioxidant enzymes in B. mori gonads.