In order to investigate effectiveness vitamin C on different characteristics of silkworm, Bombyx mori L. Silkworm larvae through 4th to 5th  instar were treated with dietary supplements of ascorbic acid 7000 (VC1) and 10000 (VC2) ppm . Leaves enriched with vitamin C were fed four times per day for the larvae. Results obtained that VC1 of vitamin C is more effective than VC2 and control. It had a significant increase in biological criteria s like larval weight and larval period while economical criteria s like cocoon weight, cocoon shell weight and pupal weight.  They weren't shown any difference between VC1 and VC2 compared to control. Ascorbic acid (VC2) significantly increased the number of Prohaemocytes (Pr) 15, Granulocytes (Gr) 35.3, Plasmatocytes (Pl) 27.6 and Oenocytoides (Oe) 8 cells, respectively. This study was indicated that vitamin C has been effective on increasing the growth rate of larvae, weight of the cocoon and increasing the immunity of larvae. So, It is recommended to using it in the breeding of silkworms and production of silk commercially.