The impact of boundary conditions (BCs) on simulations of precipitation characteristics using the Regional Climate Model version 4 (RegCM4) driven by two BCs (ERA-Interim: ERA, NCEP/DOE 2: R2) was investigated using 18 years (1989–2006) of simulations from the Coordinated Regional Climate Downscaling Experiment (CORDEX) East Asia region. The RegCM4 adequately simulated spatial distribution of precipitation over the East Asia region and its temporal variations, irrespective of the BC used. It overestimated precipitation over the central region of the model domain except for India and South Korea and underestimated precipitation over equatorial ocean regions. The RegCM4's simulation skills were better in winter than in summer regardless of the BC, which can be related to the low spatial resolution (50 km) of the model, but detailed simulations of precipitation are significantly impacted by the BCs, although the impact varies with geographical location and season. Driven by ERA, the RegCM4 reproduces more precipitation in the central inland region of the model's domain and less precipitation in the southern coastal areas than when driven by R2. The differences occur because RegCM4 driven by ERA simulated the lower troposphere as being warmer and more humid and the upper troposphere as being cooler than that by R2. The transport of moisture into the central region of the model domain is also enhanced when the RegCM4 is driven by ERA. Although the RegCM4 accurately simulated the seasonal variations in precipitation, it failed to capture diurnal variations over South Korea, particularly when driven by R2, and overestimated and underestimated light precipitation (<25 mm/day) and heavy precipitation (> 50 mm/day), respectively.