We have recently reported that red ginseng acidic polysaccharide (RGAP), isolated from Korean red ginseng (Panax ginseng C. A. Meyer), showed immunomodulatory antitumor activities, mainly mediated by nitric oxide (NO) production by macrophage. In this study, we examined the effect of RGAP on anticancer activity using lung carcinoma 3LL, sarcoma 180 and adenocarcinoma JC tumor cells transplanted into mice as well as antimetastatic activity using B16-F10 melanoma. When RGAP (300 mg/kg) were treated to mice implanted with one of the three kinds of tumor cells, the tumor weight significantly decreased compared with control mice. Tumor inhibition ratios of RGAP (300 mg/kg) in mice transplanted with lung carcinoma 3LL, sarcoma 180 and adenocarcinoma JC cells were 26.8%, 29.3% and 31.6%, respectively. Hundred mg/kg of RGAP did not cause a significant decrease in tumor weight compared with control group. When RGAP was administered i.p. with the dose of 100 and 300 mg/kg in B16-F10 melanoma-bearing mice, lung metastasis were reduced significantly in mice. Corrected phagocytic index was also remarkably increased by RGAP. These results suggest that stimulation of phagocytic activity of macrophages may be a mechanism for in vivo anticancer and antimetastasis activities of RGAP.