The combining ability and heritability of eight Chinese and eight Japanese summer-autumn rearing silkworm varieties from different ecotopes and their 64 cross combinations were analyzed in an 8×8 incomplete diallel crossing design (NCⅡ) for the following seven quantitative characters: cocoon weight, cocoon shell weight, cocoon shell ratio, cocoon crop per 10 000 4th larvae, shell weight per 10 000 4th larvae, dead worm cocoon rate and larva-pupa viability rate. The results showed that variances of the general combining abilities (GCA) and special combining abilities (SCA) of the seven quantitative characters were significant or greatly significant, and all of these characters were controlled by both additive and non-additive effects with the additive effect the principal one. Dead worm cocoon rate, larva-pupa rate and cocoon crop per 10 000 4th larvae were mainly affected by environment factors, whereas the remaining quantitative characters were mainly influenced by genetic effects. Cocoon shell ratio, cocoon shell weight and cocoon weight were the characters with high heritability, and the directional selections for them could be conducted in earlier selections. In contrast, it was better to increase selection pressures in the middle and late selection periods for dead worm cocoon rate and larva-pupa rate because of their low heritabilities. Chinese variety C5 and Japanese variety Ri3 showed high GCA effects, and the combination Ri3×C5 showed high SCA effect, indicating varieties C5 and Ri3 were superior parent materials which would be used in future breeding programs.