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 $EC_{50}$ values (0.96 mg/mL), the concentrations of the SSE that exhibit 50% reduction in DPPH, and highest scavenging of $ABTS^{{cdot}+}$ 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 $ABTS^{{cdot}+}$ radicals and the ferric reducing ability (FRAP assay).