Objective: The present study was aimed to investigate the antihyperglycemic activities of Thai silkworm (Bombyx mori Linn.) powder, fibroin and sericin from three races of Thai silkworm including Nangnoi, Nanglai, and Samrong in streptozotocin-induced diabetic rats. Materials and Methods: All rats were daily and orally administered with silkworm powder (5th-instar, 3rd-day), fibroin, and sericin at a dose of 250 mg/kg for 6 weeks. After that, various parameters including body weight, blood glucose, hematological and biochemical parameters were determined. Results: The results revealed that fasting plasma glucose level in 6th week of Nanglai fibroin, Nangnoi fibroin and Nangnoi sericin expressed a better reduction of FPG in diabetic rats compared with diabetic control groups (p<0.05). All hematological parameters of each group were not different within those values (p>0.05). In case of blood urea nitrogen, creatinine and alkaline phosphatase value showed that some of treated groups was different from diabetic control (p<0.05), while all of treated groups showed different in cholesterol and high density lipoprotein value (p<0.05). Conclusion: Silkworm powders, fibroin and sericin of three races exhibited a therapeutic potential for the reduction plasma glucose level. Treatments of silkworm powder, fibroin and sericin did not have any effect on hematological parameters. Improvement of blood urea nitrogen, creatinine, alkaline phosphatase values and lipid profiles also were also observed in the treatment groups.