Abstract: We collected 168 female Harpiosquilla harpax and dissected them individually for a comparison of their developmental features of thelycum and ovary, and for  ultramicroscopic observation of contents in the milky-white thelycum. The results show that the females had paired ovaries that lied between pericardial sinus and digestive tract, which extended from the back of the breastplate to the tail. The apparent color of ovary changed as follows: colorless−rayish yellow−earthy yellow−light yellow−orange, and the mature ovaries were orange or pink. The gonadosomatic index (GSI) were 1.62±0.53, 2.73±0.44, 3.82±0.48, 6.84±1.04 and 11.63±2.11, respectively. The females had three parallel strips that were visible through the exoskeleton at the sixth, seventh, and eighth thoracic sternites, which were organs for sperm-storage, and the apparent colours of thelycum were changeable (colorless−transparent−light white−turbidity−milk white−dense). The more mature the ovary was, the heavier milk white of the thelycum became. Group of sperms with membranes had been observed in the thelycum contents which were filled with filamentous stroma. The shape of sperm was spherical but without flagellum and acrosome, size of 1~3 μm. The results provide references for further research on the reproductive biology and artificial breeding of H. harpax.