Abstract: We calculated potential evapotranspiration (E0) using the Penman-Monteith equation and the analyzed temporal characteristics of climatic variables during the past 50 years (1961—2010) in the upper-middle reach of the Yellow River basin (UMYB). Sensitive coefficients of E0 and the contributions of climate variables to E0 in the study area were quantitatively analyzed using partial differential method. The results were as follows. 1) There was a significant increase in air temperature (α < 0.01), and a significant decrease in wind speed and sunshine duration (α<0.01). The climate of UMYB had become warmer and drier during the past 50 years. 2) The sensitivity coefficient of E0 to climate variables follows the order from high to low as actual vapor pressure (ea)>maximal air temperature (tx) > wind speed (v) > sunshine hour (SH) > minimal air temperature (tn). It was most sensitive to tx in summer and to ea in the other seasons. 3) On the annual scale, the variation of E0 was largely contributed by v, followed by tx, tn, SH and ea. The dominant factor contributing to E0 trend in spring, summer, autumn and winter was v, SH, tx and tn, respectively. The positive effects of the increase in temperature and the decrease in humidity were offset by the negative effects of the reduction in wind speed and solar radiation. Comprehensive considerations on the impacts of all climatic variables on evapotranspiration would largely improve our knowledge on climate change and provide advices for local agricultural, forest and animal husbandry production.