Frequency distribution for chromosomal P factor activity and extrachromosomal cytotype in a natural population of Drosophila melanogaster were analysed by gonadal dysgenic (GD) sterility in P-M system. The flies used in this experiment were collected from Gwacheon city in the fall, 1988 and 1989. The frequencies of P factor activity less than 10% GD sterility of initial population observed 93.94% and 98.96% in 1988 and 1989. After five month in each years the frequencies were increased as 91.92% and 100%. The distribution of cytotypes less than 10% GD sterility occurred 42.43% and 88.54% in 1988 and 1989, and after five month in laboratory condition was a little changed as 36.36% and 85.41%. From the results of GD sterility, the strain type by Kidwell et. al (1977) criteria, Q and M’ types (95.96%) were highly distribute than P and M types (4.04%) in 1988, and those for 1989 observed only 1.04% in P type and the other was Q and M’.