Bracon brevicornis Wesmael (Braconidae: Hymenoptera) is a generalist idiobiont ecto-parasitoid that parasitizes a wide range of Lepidoptera. In the present context, our study aimed to examine under laboratory conditions the effect of host size on the biological parameters of parasitoids B. brevicornis for efficient laboratory rearing of that parasitoid. Under the no-choice situation, we compared biological parameters of this parasitoid wasp on four host species belonging to the Lepidoptera, viz. Pectinophora gossypiella  (Gelechiidae) and Earias insulana (Noctuidae) as small size hosts, Helicoverpa armigera (Noctuidae)and Spodoptera littoralis  (Noctuidae) as large size hosts. The biological parameters of the parasitoid on P. gossypiella or E. insulana (Small size) in most case proved to have a significant effect on their egg-adult developmental stages compare to its interaction vs. H. armegra or S. littoralis  host (large size). The hosting on P. gossypiella or E. insulana the parasitoid produced excellent paralyzing and parasitism capacities but this capacity was less efficient on large size hosts and they received a significantly lower number of eggs as compared to H. armegra or S. littoralis which they received a good number of eggs. No variation was observed considering the egg-to-adult development time of B. brevincornis parasitizing P.gossypiella (small size) and S. littoralis (large size), but the lowest egg-to-adult development time was observed on H. armegra (large size). The biochemical analysis showed that the larger size hosts contained more resources for the growing the parasitoid, this was reflected only on fecundity. The other biological parameters: hatchability, longevity, lifetime and the percentage of hosts producing parasitoid offspring and sex ratio were not dependent on host size regardless of parasitoid generation. The results indicate that the parasite's behaviour of B.brevicornis can develop under no-choice situation equally successfully on both small and large size host.