Abstract: Thirteen Cucurbitaceae species have been investigated for anti-H activity of seed lectins. The lectin was extracted from seed powder and concentrated by ethanol precipitation method. Momordica charantia, Trichosanthes kirilowii, T. cucumeroides and T. bracteata had potent hemagglutinating (HA) activity toward human type-H(O) erythrocytes, in which M. charantia exhibited considerably lower activity toward human type-Omh (para-Bombay, H-deficient). Hence, it was characterized as anti-H activity. Eight Japanese cultivars exhibited almost same degrees of anti-H activity. A lectin from seeds of M. charantia has been purified by affinity chromatography and gel-permeation. The lectin was shown to be a glycoprotein containing approximately 10% neutral sugar, which gave a single band on native polyacrylamide gel electrophoresis (PAGE) and four bands of 31.5, 30.5, 30.0 and 28.5 kDa on SDS-PAGE under reducing conditions suggesting that the lectin is a tetramer. The HA activity was stable at 50 °C for 1 h, but sharply decreased beyond 55 °C. The lectin agglutinated human type-O erythrocytes and the agglutination was inhibited by D-galactose and its derivatives, particularly human blood type-H (O) antigen trisaccharide (Fucα1 → 2Galβ1 → 4GlcNAc). These results suggest that M. charantia seed lectin has anti-H (O) activity and D-galactose specificity. Inter-specific differences in anti-H activity of the seed among Cucurbitaceae may exist.