Abstract: Taking the enzymatic hydrolysate of Crassostrea hongkongensis as subjects, we used overloaded lactation model to investigate the effects of oyster enzymatic hydrolysate products (OEHP) on lactation of overloaded lactating rats by measuring the lactation volume of female rats, total average body mass increment of offspring, organ index of female rats, mammary gland organ index of female rats and serum prolactin (PRL). The mammary gland structure was observed by HE staining method. The results show that within 21 d of gavage, compared with control group, the increase of hourly lactation was significant in high-dose group, but not significant in low-dose group, positively correlated with the dose. The total average lactation of high-dose group increased by 57.85% (P<0.01); for low- and medium-dose groups, the lactation growth was 38.02% (P<0.05) and 17.69%, respectively. The body weight gain of young mice in high-, medium- and low-dose groups increased by 13.62%, 12.28% and 11.99%, respectively (P<0.01). There was significant difference in the body weight gain between high-dose group and medium-, low-dose groups (P<0.05). The mammary gland index had significant difference. The organ index increased to varying degrees. The PRL concentration in high-, medium- and low-dose groups increased by 41.67% (P<0.01), 26.39% (P<0.05) and 11.11%, respectively. Compared with low-dose group, the PRL concentration in high-dose group increased by 27.50% (P<0.05). In addition, the mammary gland structure of female rats in each group had been obviously enlarged and filled, which indicates that OEHP can improve the regulation of lactation within overloaded lactating rats effectively and promote lactation.