Reference crop evapotranspiration (ET₀) is a very important variable for hydrology and agriculture and has been widely applied to actual evapotranspiration and crop water requirement calculation as well as hydrological simulation. Under the background of global changes, analyzing the spatiotemporal characteristics of ET₀ can provide useful information for impact assessment of climate change on hydrology. After calculating ET₀ with Penman-Monteith equation using meteorological data from 48 stations, inverse distance weighted interpolation and Mann-Kendall test are used to analyze the spatial distribution and temporal changes in ET₀ on the Loess Plateau during 1961-2009. Results show that the annual mean value of ET₀ is 1060.3 mm; the values in the northwest region are greater than those in the southeast region and the smallest values occur in the southwest region, which is possibly caused by the regional combinations of different meteorological variables. Upward and downward trends are detected for 36 and 12 stations; however, only 30 and nine stations have increased and decreased significantly, respectively. Averaged over the Loess Plateau, ET₀ has increased significantly by 1.3 mm/a; the greatest and smallest changes are in spring and winter, respectively. ET₀ occurs abrupt change in 1994 and increases more significantly since then. The temporal trend in ET₀ is possibly caused by the evolutions of meteorological factors, especially by the downward trend in humidity and upward trend in temperature as ET₀ is most sensitive to changes in humidity and temperature on the Loess Plateau. The detected monotonic trend in ET₀ on the Loess Plateau is different from other regions and the upward trend in ET₀ is confirmed by this study. The continuous increase in ET₀ and decrease in precipitation will worsen the water shortage on the Loess Plateau; therefore, some countermeasures are necessary to mitigate the adverse impacts of climate changes.