The ultrastructure of sperm head in Chinese Rat Snake Zaocys dhumnades was observed by transmission electron microscopy. According to the changes of the structure of axenomal complex, the typical sperm head formation could be divided into four stages. StageⅠ , when the preacrosomal vesicle approached the nucleus, the particulate materials in the preacrosomal vesicle came into being an acrosomal granule at the bottom of acrosomal vesicle. As the preacrosome became bigger, the subacrosomal granule changed to fibrous material layer. StageⅡ, the spermatid acrosomal vesicle flattened and the acrosomal granules dispersed in the acrosome vesicle. The vesicle membrane merged to form a cap-shaped acrosomal vesicle. StageⅢ, the nucleus moved from the center to the cell pole, and proximal centriole, distal centriole and microtubules appeared. Mitochondria and endoplasmic reticulum moved from the center to the other cell pole. StageⅣ, a large number of microtubules gathered around the nucleus. As the diameter of microtubules around the nucleus became smaller, acrosomal complex fully developed.