Abstract: Spermiogenesis of sperm head in soft shelled turtle, Trionyx sinensis, was examined by transmission electron microscopy. The program of the formation of the sperm head was divided into five stages. Stage ? the preacrosomal vesicle occurred while the nuclear envelope developed a shallow fossa in the same side of the nucleus. A dense acrosomal granule arose on bottom of the preacrosomal vesicle when there was a fibrous layer between the nuclear envelope and the vesicle. A smaller sub acrosomal granulewas observed in the middle of fibrous layer under the acrosomal granule, which was related to the development of intra nuclear tubules. The nucleus began to move eccentrally and be out of shape. Stage ? the round preacrosomal vesicle became flat because the nuclear shallow fossa protruded out gradually. The dense acrosomal granule spread in the vesicle when the fibrous layer changed to the subacrosoal cone. Circularmanchettes developed around the nucleus while the chromatin concentrated to granules and the nucleus became smaller. There arose a gap between the envelope and chromatin. The intra nuclear tubules developed after subacrosomal granule disappeared, Stage ? the anterior part of elongating nucleus protruded out of the spermatid and covered by the flat acrosome. The implantation fossa formed at the end of the nucleus. Chromatin further condensed and the nucleus became thinner and longer. Stage ? after the chromatin concentrated to dense homogeneous phase, the nuclear protrusion formed on the nuclear shoulder. In this stage, the circular manchettereorganized to the oblique and then, the longitudinal one. The Sertoli process covered the acrosome forming ectoplasmic specialization. Stage V, the nuclear manchette dismissed and the ectoplasmic specialization disappeared. The subacrosomal gap occurred. The results showed that there were some differences of the spermiogenesis between Trionyx sinensis and other reptiles in the process of the chromatin condensation,the formation of the acrosome and the development of the intranuclear microtubules.