The genetic variabilities of second chromosomes of Drosophila melanogaster concealed in On-yang natural Population have been analyzed by the Cy/Pm method and an allelism test during two years(1993-1994). The mean frequencies of deleterious(lethal and semilethal) genes in On-yang natural population were estimated to be 23.97% in 1993 and 27.15% in 1994, respectively. The allelism rates between lethal genes in the population were 0.654%(1993) and 1.429%(1994). The mean values of elimination by frequencies of deleterious genes and allelism rates were 0.0004(1993) and 0.0010(1994), respectively. The frequencies of phenotypic sterility of males in 1994 were estimated to be 1.95%, and thoses of genotypic sterility of females and males were estimated to be 1.54% and 2.31%, respectively.