Antitumor activity of lactobacilli on Sarcoma 180 was investigated and was shown to be different from strain to strain. In general, Lactobacillus casei had higher antitumor activity compared with other species of lactobacilli. Among these, L. casei YIT 9018 (LC 9018) had significant antitumor activity against Meth A fibrosarcoma when administered into BALB/c mice intravenously, intraperitoneally, subcutaneously, intratumorally or orally. LC 9018 showed antitumor activity against rat ascites hepatoma by intravenous or oral administration, but this activity was lower than that against Meth A in mice.