The lectin from starfish, Asterina pectinifera, was purified and tested for its potential antitumor activity. It was shown to possess considerable toxicity toward various tumor cell lines. Concentration of Asterina pectinifera lectin (APL) at 4mg/$5{ imes}10^5$ cells resulted in 28% death of Ehrlich ascites tumor cell, 40% of L929, 60% of A549, and 52% of HeLa cells after 48 hours incubation. Toxicity of APL to L929, Ehrlich ascites, A549, and HeLa cells revealed a reduction in cell viability of approximately 70% at APL concentration of 8mg/$5{ imes}10^5$ cells after 48 hours incubation. Administration of APL ($100{mu}g/day$ or $300{mu}g/day$) inhibited the growth of Ehrlich ascites cells in vivo. Mice given only Ehrlich cells survived an average of $15{pm}1$ (S.E.) days. Mice given Ehrlich cells and $100{mu}g;or;300{mu}g$ APL had 58% and 67% survival, respectively, after 20 days. These results suggest that APL has antitumor activity.