Abstract: Enzymatic modification of silk fibroin was carried out by using tyrosinase and a natural antioxidant of catechin via covalent reaction between catechin and primary amine groups of silk fibroins. Spectrophotometry was used to evaluate the efficacy of adsorption and grafting of catechin onto the fibroin surfaces. The parameters like color depth, UPF value, antioxidant ability (DPPH method) and mechanical behavior for the catechin-treated silk fabrics were investigated, respectively. The results indicated that catechin could be enzymatically oxidized and conversed into dark quinone products. The color depth and UPF value for the treated sample were higher than that of the control, while less strengthen changes were detected before and after enzymatic treatments. Furthermore, both catechin treatment and tyrosinase/catechin treatment improved the antioxidant ability of silk fabrics against DPPH radical, more satisfactory result was achieved for the sample based on the combined treatment with tyrosinase and catechin.