Abstract: Molecular orbital indices of gossypol, 8-hydroxy quinoline. salicylaldehyde, salicylic acid, o-vanillin, vanillin, 2, 3, 4-trihydroxybenzaldehyde and guaiacol were calculated by means of Huckel's molecular orbital (HMO) method. It was found that the nucleophilic superdelocalizabilities of. maximally positively charged hydroxyl oxygen of these componds were correlated with their spermatocidal action in rat cauda epididymis.Moreover, as the polyacrylamide gel electrophoresis of healthy human semen treated with the above spermatocidally active compounds shows protein patterns qualitatively distinguishable from those treated with spermatocidally inactive compounds (except guaiacol) and normal semen, there exists in the above compounds fair accordance among the nucleophilic superdelocalizabilities of particular oxygen atoms, the spermatocidal action and the influence of semen protein motilities.A probable mechanism of the spermatocidal action of the compounds described above was proposed.