A description is made of the dovelopmental stagcs (from egg to adult) of Bivagina tai (Monogenea: Microcotylidae). The egg hatched at water temperature of 10-30°C. Average time required for hatching was 26.2, 11.4 and 6.8 days at 10, 20 and 30°C, respectively. The hatching rate was high (68-88%) between 10 and 25°C, but only 29% at 30°C, suggesting a high temperature is unfavourable for hatching. The genital organs of B. tai on the gills of the host developed along with the increase in the number of clamps. In most cases, the genital organs first appeared at clamp number 30-40, and fully developed at around 80. The clamp number kept increasing after maturation (≤131). Apparently, the relationship between the genital development and the clamp number was not influenced by the host fish size and water temperature.