Glaciers are of crucial importance for the livelihood of the local populations, which depend on their meltwater for water and energy supplies. For this reason, seasonal variations of oxygen-18 of glacial stream water and their sources within a small glacial catchment in south western China were investigated during the wet season. The results showed significant difference of oxygen-18 existed among meltwater, rainwater, ground water and stream water, and significantly seasonal variation of precipitation occurred during the observed period. The streamflow of Baishui catchment was separated into components of ice-snowmelt and precipitation using oxygen-18. As shown by the result of the two-component mixing model, on average, 53.4% of the runoff came from ice-snowmelt during the wet season, whereas the remaining 46.6% were contributed by precipitation in the catchment. According to monthly hydrograph, the contribution of snow and glacier meltwater varied from 40.7% to 62.2%, and that of precipitation varied from 37.8% to 59.3% in wet season. Uncertainties for this separation were mainly caused by the variation of tracer concentrations. The roles of glacier and snow meltwater should be noticed in water resource management in those glacial regions in south western China. Copyright © 2012 John Wiley & Sons, Ltd.