In order to identify organs, ovarian development and reproductive biology closely related to reproduction, observations on reproductive system, ovarian development progress and fecundity of coconut leaf beetle, Brontispa longissima were conducted in the laboratory. The results showed that the male internal reproductive system of adult is composed of testes, seminal vesicle, vas deferens, accessory gland, and ejaculatory duct. The seminal vesicle is developed from specialized vas deferens. The male external genitalia is consists of three parts, namely aedeagus, manubrium and tegmen, but have no clasper. The female internal reproductive system of adult is composed of ovary, lateral and median oviduct, spermatheca, and bursa copulatrix. The two ovaries are symmetrical, each consisting of 5 panoistic ovarioles. The female external genitalia is composed of dorsovalvula, intervalvula, and ventrovalvula. Ovarian development can be divided into 4 grades based on the morphological characteristics of ovaries, including nooocyte stage, egg maturation stage, ovipositing stage , and post-ovipositing stage. Each stage shows significant differences in the length of ovarian zones and egg-carrying number. In addition, range changes of daily fecundity of coconut leaf beetle on Cocos nucifera is minimal (2.39 egg/female), and their oviposition period is longest (348 d) comparing to other host plants, so the stable egg production is expected if coconut leaf was used in rearing. However, on the Caryota ochlandra, pre-oviposition and longevity of coconut leaf beetle are shorter, but their egg production is highest which indicated that Caryota ochlandra was ideal rearing material for fecundity of coconut leaf beetle .