[Objectives]  To improve understanding of the phylogenetic relationships between insects and ladybird taxonomy in particular, and promote the study of artificial diets in ladybirds. [Methods]  The reproductive system and oogenesis of the ladybird Cryptolaemus montrouzieri Mulsant were investigated. An optical microscope was used to observe paraffin sections of the reproductive system, and different stages of ovarian development and oogenesis. [Results]  The male reproductive system includes two pairs of paragonial glands, a pair of testes, a pair of vas deferens, a pair of seminal vesicles, an ejaculatory duct, penis and tegmen. The female reproductive system includes two genital plates, a genital chamber, spermatheca, a median oviduct, a pair of lateral oviducts, and ovaries. There are between eleven to fourteen telotrophicovarioles per ovary. The terminal filament is on the top of the ovariole, which is divided into a germarium and vitellarium. Nurse cells fill the germarium, and oocytes at the base of this obtain nutrition from the nurse cells via a nutritive cord. Nurse cell nuclei almost occupy the majority of the cell and there are no syncytiums in the germarium. Based on variations of oocyte position and characteristics, follicle cells, and yolk deposition, the process of oogenesis can be divided into a prime, middle, transitional and post-period. In the post-period, the nutritive cord has disappeared and the gap between follicle cells is distinct. [Conclusion]  Nurse cells of C. montrouzieri are one of the three types known as the primitive, transition and secondary stages. We suspect that the nurse cells of ladybirds are of the primitive stage. In the early stage of oogenesis, the main way oocytes obtain nutrition from nurse cells is via nutritive cords