The mill moth, Ephestia kuehniella Zeller and Indian meal moth, Plodia interpunctella (Hubner) are two injuriously important pests of stored products worldwide. Harobracon hebetor (Say) has been used as a biological control agent of moth’s larva in peanut storehouses and as well in packaged cereal products. In the present study, the efficacy of H. hebetor in parasitizing larva of the mill moth and of the Indian meal moth was evaluated at different densities of parasitoid (1, 2 and 4 pairs) and host larvae (1, 2, 4, 8, 16 and 32) in a growth chamber set at 25±1 °C, 65±5 RH, and 14L:10D photoperiodism. When one pair of parasitoid released, the number of eggs laid was increased at the densities of 1, 2, 4 and 8 larvae of either host, respectively but, it decreased at the densities of 16 and 32 larvae of either host. Also, the number of emerged females and adults of wasp were increased at the densities of 1, 2, 4 and 8 larvae of both hosts, respectively but, did not significantly increased at the densities of 16 and 32 larvae of either host. When two pairs of parasitoid were released, the highest number of eggs laid was observed at the density of 16 larvae of the mill moth. Whereas, the number of eggs laid at the densities of 4, 8, 16 and 32 larvae of the Indian meal moth were significantly higher than those for the other larval densities. Also, the number of emerged females and adults of wasp increased at the densities of 1, 2, 4, 8 and 16 larvae of either host, respectively but, they did not significantly increase at the density of 32 larvae for either host. When four pairs of the parasitoid released, the number of eggs laid at the densities of 8 and 16 larvae of either host was found significantly higher than those for the other larval densities. Also, the number of emerged females and adults of wasp increased at the densities of 1, 2, 4, 8 and 16 larvae of either host, respectively but, did not significantly increase for the density of 32 larvae in either host. Based on the results obtained it can be concluded that at one pair of parasitoid treatment, a number of 8 larvae of either host, at the two and four pairs of parasitoid treatments, a number of either 16 or 32 larvae of either host form the most suitable combinations for a mass rearing of H. hebetor.