Abstract: The biological investigation of Parafossarulus eximius was undertaken at Poyang Lake during February, 1985-January, 1986.The sex ratio (female: male) in nature is 1:0.69. The mating season is from late October to June of the next year and the period of ovulation is from February to August. Generally, eggs start hatching in early May and the juveniles attain sexual maturity in the same year, but ovulate and breed in the next year. Four- or five-month old juveniles attain to 13—15 mm in height. They stop growing in October owing to the lowering temperature and grow again in the next May or June when the climate becomes favourable. The biggest shell is about 18 mm high. The relationship between shell height and shell width is linear, while those between shell height, shell width and wet weight are exponential. P. eximius is recorded for the first time as an intermediate host of a trematode.