Abstract: Objective:To investigate the anxielytic-like activity of enzymatic hydrolysate of Undaria pinnatifida. Methods:Fifty male ICR mice were randomly divided into five groups,ten mice per each group:the control group,Diazepam(2 mg/kg),enzymatic hydrolysate of Undaria pinnatifida(1 g/kg),enzymatic hydrolysate dialysate(1 g/kg)and enzymatic hydrolysate dialysis residual(1 g/kg). The contents of dopamine and 5-hydroxytryptamine were tested by ELISA measurement after long term oral administration. Results:Enzymatic hydrolysate dialysate group significantly increased the visits and the time in open arms(p<0.01),respectively. And Enzymatic hydrolysate dialysate group(p<0.05)reduced the content of 5-hydroxytryptamine in mice brain tissue after long term administration. However,there was no significant change on the content of dopamine(p>0.05). Moreover,enzymatic hydrolysate group and enzymatic hydrolysate dialysis group showed no significant effect on the visits and the time in open arms(p>0.05),respectively. And there were no significant changes on the content of 5-hydroxytryptamine and dopamine(p>0.05). Conclusion:Enzymatic hydrolysate of Undaria pinnatifida,of which the molecule weight was below 6 kDa,showed the anxiolytic-like activity. The mechanism might be associated with the content of 5-hydroxytryptamine in ICR mice brain tissue.