The results of some aspects of the reproductive biology of MystusnaacSa-oterus f Bleeker )，based on 928 specimens from the Jiz Ling River during theperiod of May I9$fi to December 1987，are aummaried in this paper. Results ofthis study provide strong evidence that the ovaries，based an both external and hi-stolagical features, are divided into sex maturation stages. The spawning season of.the fish starts from May to July. The female is confirmed to spawn once in spaw-ping seasVn. After spawning, the ovaries of the fish remain at the stage III andpass through the whole winter. Spermatids are commonly found in the testes of theoverwintering males. Accumulion and consumption of fat is greatly related to thedevlopnient of gonads. Sex ratio is. 0.93:1，a little in favor of male. Age-and-sizefirst, maturities of male anal femsle are 2 and 3 years old with.body length ofL4.5em and 1T .8cm respectively. .4-and 5-year old fish account For the 50% of thespawning population.