The present study investigates the phenolic contents and antioxidant activities of silk sericin extracted (SSE) from Thai mulberry silkworms (Bombyx mori) and non-mulberry silkworm (Samia ricini). The SSE from all strains revealed the mainly presence of flavonoid compounds including (+)-catechin (20. 63-145. 64 mg/100 g), quercetin (7. 89-35. 95 mg/100 g), and (-)-epicatechin (3. 36-44. 19 mg/100 g). The antioxidant activity of the SSE with water from Chokumnoui 1 was found to have low EC50 values (0. 96 mg/mL), the concentrations of the SSE that exhibit 50% reduction in DPPH, and highest scavenging of ABTS^{· +} radicals (1. 73 mg TEAC/g) and highest reduce TPRZ-Fe (III) complex to TPTZ-Fe (II) (8. 03 mg Fe(II)/g), thus indicating high antioxidant activities. Total phenolic content and total flavonoid content of the SSE showed positive correlated to the scavenging activity of DPPH and ABTS^{· +} radicals and the ferric reducing ability (FRAP assay).