Abstract: Heterosis and combining ability studies of the isolated variable multivoltine races and developed bivoltine races with high yield capacity and their eighteen combinations were evaluated in two commercial rearing seasons in Bangladesh. Appropriate statistical methods were employed to interpret data on the hybrid performance, general and specific combining ability of the hybrids. Analysis of variance for combining ability revealed larger mean squares. Here high δ2gca/δ2sca values for most of the characters reflected predominant additive gene action. Similarly, the variance of components of specific combining ability (δ2sca) of multivoltine×bivoltine were higher than those of general combining ability (δ2gca) for most of the characters in both the seasons indicating preponderance of non-additive gene action inheritance of all these traits. Among the combinations BSR-BN(B1)×BSRB-BB1 and BSR-3×BSRB-BB2 exhibited highly productive performance which could be recommended for commercial cocoon production in Bangladesh.