The silkworm powder (Bombyx mori Linn.) from Japanese and Korean races has well known used as a blood glucose lowering substance. However, the study of bioactive compounds and hypoglycemic effect on Thai silkworm races is still limited. This study was aimed to investigate the flavonoid, phenolic and 1-deoxynojirimycin (DNJ) contents, and α-glucosidase inhibitory activity of three Thai silkworm races (Nanglai, Nangnoi and Samrong) of the 5th instar, 2nd 4th day silkworm powders. The total flavonoid, phenolic contents and α-glucosidase inhibitory activity were performed using spectrophotometric methods. The DNJ content was determined using derivatization and further analyzed by HPLC. Nangnoi showed the highest flavonoid content with 12.32±0.41mg quercetin equivalent/g silkworm powder. Nanglai showed the highest phenolic content with 78.74±1.43mg gallic acid equivalent/g silkworm powder. Regarding DNJ content, Nangnoi expressed the highest at 3.11±0.01mg/g silkworm powder. According to the age of silkworm, powders of the instar 5th, day 3rd were provided the highest α-glucosidase inhibitory activity (p<0.05). This study clearly indicated that the 5th instar, 3rd day of Thai silkworms exhibited the highest flavonoid, phenolic, DNJ contents and α-glucosidase inhibitory activity. Further study on blood glucose lowering activity should be performed.