In the experiment, gene actions were analyzed for seven silkworm varieties in order to obtain basic information on their genetic improvement by diallel crosses. The results obtained were summarized as follows : in analysis of variance, significantly maternal and reciprocal effects were observed for all character except female cocoon shell percentage and female pupal weight. Over-dominance was shown by Vr-Wr graphic analysis in three characters such as female cocoon weight, female and male pupal weight, and partial dominance in five characters such as male cocoon weight, cocoon shell percentage in both female and male. Component of genetic varience analyzed for five characters such as male cocoon weight, cocoon shell weight, cocoon shell percentage in both female and male showed that additive effects were higher than dominant effects, and female cocoon weight showed dominant effects higher than additive effects. Heritability of narrow sence was higher more than 0.51 and heritability of broad sence was higher more than 0.77 in all characters except for female pupal weight. The directions of dominance were negative for female cocoon shell weight and somewhat higher for female and male cocoon shell percentage. Meanwhile cocoon weight, pupal weight in both female and male showed positive in the direction of dominance.