The chromosome constitution of complete hydatidiform moles (CHM) is Known to be 46, XX with genetically 100% homozygosity, which is being derived by androgenetic mechanisms. The present study was undertaken to find a mechanism among three possible androgenetic derivations: 1) duplication of a haploid sperm after fertilization with anucleated egg, 2) fertilization of a diploid sperm due to nondisjunction at second meiotic division, 3) fertilization of two haploid sperm simultaneously. Our results obtained from RFLPs and DNA fingerprinting techniques showed that the genome of CHM is derived by duplication of a haploid sperm. This is in accord with the hypothesis proposed from the experimental results using cytogenetic banding techniques (Jacobs et al., 1978; Lawler et al., 1978, 1982, Vejerslev. et al., 1978) and polymorphic enzyme markers (Jacobs et al., 1980; Lawler et al., 1982; Vejerslev et al., 1987), and also using HLA typings & Yamashita et al., 1979; Coullins et al., 1985; Vejerslev et al., 1987).