Objective Propylea japonica is an important natural enemy of agriculture and forestry, which can prey on aphid, whitefly, psyllid and other pests. The study of the reproductive system and oogenesis of P. japonica will provide scientific data support for its artificial breeding.

Method The reproductive system and oogenesis of the P. japonica were observed with optical microscope by paraffin section technique and anatomical method.

Result The male reproductive system include 1 pair of testis, 1 pair of paragonia glands, 1 pair of vas deferens, seminal vesicle and ejaculatory duct. The female reproductive system include 1 pair of ovaries, 1 pair of lateral oviducts, median oviduct, spermatheca and gential chamber. Each side of ovary contains 11-13 ovarioles. According to the yolk precipitation and the morphology change of follicle cells, oogenesis can be divided into prime, middle, transitional and final stage.

Conclusion The structure of ovary, the numbers of ovarioles and oocytes help to explain the oviposition quantity of P. japonica. Unsuitable rearing conditions may inhibit the development of ovary and lead to the change of oviposition quantity. Therefore, in order to realize the large-scale application of P. japonica, the optimal nutritional and environmental conditions should be created to ensure the production of as many mature eggs as possible.