Scanning electron microscopic observations were made on the morphological structures of the two copulatory spicules of the male Necator americanus and Ancylostoma duodenale. In both species,one of the two copulatory spicules was in the shape of a concave groove and the other, in the shape of an oblate tube. Owing to the difference in the concavity of the groove shaped copulatory spicule between the two species as shown by the cross sections, Necator americanus usually appear to have only one copulatory spicule whereas Ancylostoma duodenale usually show two separate copulatory spicules in appearance (Figs 1 -10).