In sericulture fungicides are applied for two purposes; (1) to heal the fungal diseases of mulberry trees and (2) to prevent and control fungal diseases, such as muscardine, of silkworms (Kuberappa and Jayaramaiah, 1988). Therefore identifying appropriate fungicides with a high efficiency of disease control with low side effects on silkworm are very important. Lin and Tzeng (1994) reported that alpha-DL-difluoromethylornithine (DFMO) treatment showed no deleterious effect on mulberry plants and treated plant parts were safe to use as feed for the silkworms, even immediately after application. The fungicide carbendazim belongs to the benzimidazole class and is recommended to control muscardine and mulberry powdery mildew. Azole fungicides, such as triazoles and imidazoles, are molecules that inhibit ergosterol biosynthesis by preventing the cytochrome P-450 dependent 14 alpha-demethylation of lanosterol. These can also inhibit the cytochrome P-450-dependent metabolism of both endogenous and exogenous compounds (Kuribayashi, 1988). Because carbendazim has recently been introduced to sericulture the present study aimed to investigate the effects of long term application of carbendazim on the biological performance of silkworms.