【Background】Procecidochares utilisStone (Diptera: Tephritidae) is an important obligate enemy of Eupatorium adenophorum Spreng.. The larvae of flies can bore into the E.adenophorum leading to gall formation, which can effectively restrict the dispersal of E.adenophorum. It is considered an effective biological agent to E.adenophorum. Many countries have used this insect to control the damage caused by E.adenophorum. 【Method】The structure and development of internal reproductive organs in adult P.utilis were extensively analyzed by optical microscopy method. 【Result】The internal reproductive organs of female adult P.utilis were composed of ovaries, lateral oviduct, spermatheca, female accessory glands; and male internal reproductive organs were composed of testes, vasa deferentia, male accessory glands and ejaculatory duct. During the development, the maximal length and width of ovaries were reached at 4 and 1 dayold respectively. While the size of the female accessory glands and spermatheca did not vary significantly among females of different ages, length and width did. The maximal length and width of testes were reached at 4 and 2 dayold respectively. Similar to the females, size of the male accessory glands did not significantly vary among age groups but length and width showed significant variation. 【Conclusion and significance】The study examined the structure and development dynamics of internal reproductive system in P.utilis. For the results can be useful to improve the breeding efficiency of P.utilis and the effects of biological control against E.adenophorum.