Precipitation is an important element in the hydrological cycle in mountainous regions. Temporal and spatial variations in precipitation and in its two phases – rain and snow – over the northern and southern aspects of the slopes of the Tianshan Mountains are compared and analyzed using 55-year data (1961-2015). The results of the analysis are as follows: 1) The average annual precipitation shows an upward trend: rainfall on the northern slopes increase by 6.7 mm per decade and that on the southern slopes by 6.4 mm per decade; the corresponding figures for snow are 2.0 mm and 4.2 mm; and the ratio of snowfall to precipitation (S/P) showed a weak decreasing trend on both the slopes. 1) At a confidence level of 0.05, the M-K test shows that rain, snow, and S/P increased after the change point, while rain and snow change significantly in the proportions,but S/P does not. 2) On the northern slopes, the periodicity of major changes is 25 years for rain and 30 years for snow, whereas on the southern slopes the pattern is the exact opposite, the periodicity of major changes being 25 years for rain and 30 years for snow.