Artificial diploid gynogenesis, a form of all-female inheritance, was considered as one of the most effective techniques for the rapid establishment of inbred lines, mono-sexual broods or clones, as well as for examining sex-determination and gene-centromere recombination. Induction of gynogenetic diploid in many mollusks has been performed recently, but few cytological studies have depicted the fertilization and early cleavage events in eggs inseminated with ultraviolet （UV）-irradiated sperms. The aim of the experiment was expected to examine the differences of nuclear behavior on early development between normal and artificially induced gynogenetic diploid eggs of Chlamys farreri. In this study, a large number of gynogenetic diploids in Chlamys farreri were generated by activation of eggs with UV-irradiated spermatozoa and subsequent diploidization of the maternal chromosome set by blocking the second polar body extrusion. The optimal dose of UV light irradiation at intensity of 800 μW?cm^- 2?s for 50 s and the best treatment condition of 60 mg?mL^-1 6-dimethylaminopurine（6-DMAP）for 20 rain were obtained on the basis of the preceding trials. Then, to treat normal and gynogenetic diploid eggs of C. farreri fixed in Bouin＇ s fixative, nuclear changes were observed carefully under an optical microscope during fertilization and early cleavage. The results of cytological observation indicated that the female and male pronuclei of normal eggs fused into zygotonuceus, but their behaviors of gynogenetic diploid eggs were considerably complicated. The sperm nucleus of gynogenesis had at least two situations： One was that it kept dense and could not develop into male pronucleus, and another was that it expanded again after the second meiosis but did not reach its maximum as a normal male pronucleus. In the process of the first and second cleavages. The sperm nucleus of gynogenesis, which became a dense chromatin body （DCB）, did not participate in the karyokinesis and was located between the two maternal chromosomes. At the completion of cleavage, DCB was seen either in the region of the first cleavage furrow or in the cytoplasm of one of the two blastomeres. Treatment with 6-DMAP, the formation of the second polar body was inhibited effectively and diploid female pronucleus was formed. In addition, the phenomena of polysperm and polyspindles in the experiment were also observed and analyzed.