The general and specific combining abilities and hybrid vigour of seven polyvoltine breeds [BL24, BL62, BL6S, BL67, BL68, BL69, and Pure Mysore (PM)] with five bivoltine breeds (NB4D2, CSR2, CSR5, CSR18 and CSR19) were evaluated in a line ${times}$ tester design by analysing six quantitative traits viz., fecundity, yield 110,000 larvae both by number and weight, cocoon weight, shell weight and cocoon shell ratio. ANOVA estimates showed significant effects for all the traits indicating the role of both additive and non- additive gene actions. Estimation of GCA revealed that the breed BL67 exhibited significant positive effects toy all the six traits followed by BL68 for four important economic traits viz., fecundity, cocoon weight, shell weight and cocoon shell ratio. Among testers, CSR5 showed significant GCA effects for five traits whereas CSR2 exhibited for shell weight and shell ratio. Three hybrids viz., BL67${times}$ NB4D2, BL67 ${times}$CSR5 and BL67${times}$ CSR19 excelled in four quantitative traits for SCA. Majority of the hybrids expressed positive hybrid vigour for cocoon yield/10,000 larvae by weight, cocoon weight and shell weight. Four hybrids namely PM ${times}$ NB4D2, BL67 ${times}$NB4D2, BL67${times}$ CSR5 and BL67${times}$ CSR19 manifesting positive hybrid vigour for five economic traits were adjudicated as best Heterotic hybrids and recommended for commercial exploitation to increase the silk yield.