Glutathione S-transferases (GSTs, EC 188.8.131.52) are a family of super enzymes with multiple functions that play a major role in the detoxification of endogenous and xenobiotic compounds. In our previous study, we have predicted 23 putative cytosolic GSTs in the silkworm genome using bioinformatic methods. In this study, we cloned and studied the insect-specific epsilon-class GST gene GSTe4 from the silkworm, Bombyx mori. The recombinant BmGSTe4 (Bac-BmGSTe4) was overexpressed in SF-9 cell lines, and it was found to have effective GST activity. We also found that the expression of BmGSTe4 was especially down-regulated after the silkworms were fumigated with or ingested phoxim. Moreover, BmGSTe4 protected HEK293 cells against UV-induced cell apoptosis. These results demonstrated that BmGSTe4 has GST activity, is sensitive to phoxim, and plays a role in inhibition of UV-induced cell apoptosis.