Fish intestine is a byproduct of fish, which is often discarded and causes environmental pollution. In this study, the hydrolysates, with Hydroxyl-Radical-Scavenging Activity (HRSA), were prepared grass carp intestine protein by hydrolysis with complex enzyme. The hydrolytic process was monitored by HRSA and the hydrolysis conditions were optimized as follows: reaction time of 2 h, temperature 50°C, pH 6.5 and 12 mg complex enzyme 50 U/g protein. Under these conditions, maximum HRSA was obtained. The Protein Hydrolysates (PHs) were fractionated into four ranges on the basis of molecular weight using a gel column chromatography. Results indicate that PHs in the PH3 induced the highest HRSA.