Genetic relatedness and the breeding structure of a Japanese paper wasp.Polistes jadwigae, population was studied using electrophoresis ol adults collected from 1985 to 1988. Mean genetic relatedness among female offspring was estimated to be 0.729 when data for 4 years were combined. This value was not significantly different from a hypothetical value (0.75) for the case where one single-mated queen is the mother of all female progeny. No sign of inbreeding was detected. Mating frequency of queens estimated by using the goodness of fit test on Chi-square distribution and the ANOVA method, also suggests that it was most probable that female progeny ofP. jadwigaecolonies were produced by a single queen mated only once.