This study was carried out to elucidate the genetic influence of the eight-fold magnetic field on selective disadvantage between yellow bodied-white eyed mutant and the wild type of Drosophila melanogaster collected at Keojedo in Korea. Fro the present experiment using population cages, each fly of two cages reared under the influence of two different strength of magnetic fields, i.e., the ambient and the eight-fold magnetic field.. Through Duncan's multiple range test and LSD value, the highly significant differences between the wild type and any one of the other three mutants were calculated. The mean selective frequencies of wild type allele up to twenty-fifth generation, affected by two different magnetic fields, showed 0.7301 and 0.7265 with the magnetic fields strength as mentioned magnetic order before. The data explains that Drosophila melanogaster population reared in the eight-fold magnetic field generated by Helmholtz coils shoed stronger selective disadvantage. The mean frequencies of the mutant carrying yw allele showed 0.0273 and 0.0234 by the same order of magnetic field strength indicated above it was shown that the fly population reared at the eight-fold strength cleared the relatively strong selective disadvantage being 0.0234, however the opposite value was 0.0273 resulted from the ambient magnetic field. The over-all mean emergence rates of Drosophila melanogaser populations reared in controlled magnetic fields, that is, the ambient and the eight-fold showed 40.05% and 59.95%, respectively. Referring to these data, the fly population raised in the ambient magnetic field showed a relatively lower emergence rate than the eight-fold magnetic field population.