The testis formed of 4 follicles develops as a definitive organ on the first day of IV instar. The localization of Δ5-3β-hydroxysteroid dehydrogenase. 17β-hydroxysteroid dehydrogenase and 11β-hydroxysteroid dehydrogenase, was limited to peritoneal sheath and epithelial layer of the testis of IV and V instar larva. From 3rd day of pupation upto the 8th day of pupation the enzyme activity extended to the cysts containing spermatogonical cells, primary and secondary spermatocytes and subsequently to the spermatids and spermatozoan bundles from 9th day of pupation and continued thereafter in the adults. Glucose-6-phosphate dehydrogenase activity was observed in all the testicular components during larval, pupal and adult stages. These results indicate that the developing and adult testis of eri silkworm,Philosamia ricini has the ability to metabolize hydroxysteroids.