Great efforts have been made to explore the potential treatment for cancers, and the most common therapies include surgery, chemotherapy and radiotherapy. As an alternative medication, earthworms have drawn increased attention considering its abundance in resource, easy access and minor side effects compared to traditional therapies. However, few studies had focused on the antitumor effect of earthworm-derived components. The purpose of this study is to investigate whether earthworm extract has an effect on tumor cell apoptosis and growth. Earthworm extract (EE) was purified through multiple steps of centrifugation and chromatography. Mice were inoculated with ascitic fluid derived from mice inoculated with S180 sarcoma tumor cells and fed orally with different amounts of EE for 25 days. Tumor samples were analyzed for size and cell apoptosis. And we found that the weight and sizes of tumor decreased gradually as the amount of EE administered increased. More apoptotic cells and lowered level of lactate dehydrogenase (LDH), a biomarker of tumor invasiveness, was detected in EE-treated group than the untreated group. Our results suggested that EE could dramatically promote tumor apoptosis and reduce tumor size in vivo, suggesting a novel alternative therapy for cancer patients.