The temporal and spatial variations of mass balance on different timescales were analyzed to identify their response to climate change using long-term observed mass-balance data covering the period 1959–2002 at Ürümqi glacier No. 1 at the headwaters of the Ürümqi river, Tien Shan, China. The results show that the accumulated glacier mass balance has decreased by 9599 mm w.e., which is equivalent to about 10 m mean thickness reduction. The negative mass balance has been accentuated in recent years, with a mean mass balance during the period 1997–2002 of –739.6 mm a−1. The glacier mass balance shows a clear periodicity, with positive and negative alternations of 7 and 15 years during the past several decades. Annual mass balance shows a significant negative correlation with summer air temperature from June to August. It is influenced more by annual air temperature than by annual precipitation. The temperature increase preceded the precipitation increase as an influence on the mass balance. Furthermore, monthly mass balance shows a negative correlation with monthly air temperature, significant at the 99% confidence level in July and August. Monthly mass balance is negatively correlated with precipitation in May and August at the 95% confidence level, but positively and insignificantly correlated with precipitation in June and July. The negative relationship between mass balance and precipitation might be related to concurrent increases of precipitation and temperature.