In this experiment, gene action 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 F1 generation, over-dominance was shown by Vr-Wr graphic analysis in four characters such as cocoon length in female, bave weight, cocoon weight and boiling off ratio in both male and female, and partial dominance in four characters such as fifth instar period, cocoon layer weight, cocoon layer ratio and bave length. In F2 generation, the partial dominance in all characters were obtained. Components of genetic variance analyzed for five characters such as fifth instar period, cocoon width, cocoon layer weight, cocoon layer ratio and fibroin contents in F1 generation, and for four characters such as cocoon width, cocoon layer weight, cocoon layer ratio and frbroin contents in F2 generation showed that addition effects were higher than dominant effects.