To investigate the in vivo effect of a seashell protein Haishengsu (HSS) on Ehrlich ascites tumor, mice were inoculated with Ehrlich ascites tumor cells. They were randomly divided into three HSS groups and control group. The survival times in the three HSS-treated groups was longer than in the control (P<0.01) and the increased life span in the high dose HSS group was greater than in the lower dose groups (P<0.05). In comparison with control group, the mice receiving pretreatment of HSS had longer survival times and greater life spans following inoculation of the ascities tumor (P<0.05). In conclusion, HSS prolongs survival times and increases the life spans of Ehrlich ascites tumor bearing mice. Pre-treatment with HSS also diminishes the detrimental effect of Ehrlich ascites tumor on the prognosis of these animals.