Abstract: Glyptosternon maculatum is an endemic Tibetan catfish that comprises an important part of local fishery.The present study describes and characterizes the reproductive biology of female and male G.maculatum,based on monthly samples taken off Lhasa River,the largest tributary of Yarlung Tsangpo River,from November 2004 to September 2006.Annual changes in gonadal histology,gonadosomatic index (GSI) and size-frequency distribution of oocyte were studied.The results of gonadal histology analysis showed that the development of gonads could be divided into six stages.The gonad of stage Ⅵ in the spawned female degenerated into stage Ⅲ from June to July,and then gradually developed into stage Ⅳ in August to September,the gonad remained at stage Ⅳduring winter (from October to March of next year),and gonad developed into stage Ⅴ during April and May and spawned in May to June.GSI values for females increased in April,reached to the peak in May,and declined in June,and then increased slowly during June to September.Therefore,G.maculatum have a short spawning season (April to May) in Lhasa River as determined from GSI values and histological assessments.The youngest mature male was age 5 with a standard length (L) of 141.7 mm,and the youngest mature female was age 5 with the L of 146.8 mm.The standard length at which 50% of the individuals attain sexual maturity (L50) was 170.1 mm for males and 150.2 mm for females.The size distribution of oocytes,with at least two groups of ooctes in the ovaries,but this fish spawns only once a year,and all of mature eggs in the ovary will be laid out during spawning.In 19 pre-spawning females (the standard length ranged from 151.0 to 210.0 mm),the absolute fecundity ranged from 525 to 2058 eggs,with a mean value of (1244±346) eggs,and the relative fecundity was (14.7±5.8)eggs/g.A linear relationship existed between absolute fecundity (F) and L: F=13.624L?118.