A fully coupled regional ocean-atmosphere model was used to simulate the East Asian summer monsoon (EASM) precipitation. This coupled regional climate modeling system consists of the Regional Spectral Model (RSM) for the atmosphere and the Regional Ocean Modeling System for the ocean. The ocean and atmosphere share the same horizontal grid resolution. The coupled model is forced by the National Centers for Environmental Prediction-Department of Energy (R-2) global atmospheric reanalysis and Simplified Ocean Data Assimilation global oceanic reanalysis through the lateral boundary. This study examines EASM surface oceanic state and precipitation variability from a 22-year (1984–2005) integration with a horizontal resolution of 40 km. The coupled model captures the features of observed sea surface temperature (SST), sea surface height, and ocean surface currents. Compared with the control run of the uncoupled RSM forced with observed SSTs, the coupled model shows more realistic simulation of the EASM precipitation climatology. The coupled model also improves the simulation of precipitation variability at both interannual and intraseasonal scales. It is the coupled model, not the uncoupled RSM, represents the observed SST-precipitation and SST-evaporation relationships. This study indicates that the ocean-atmosphere coupling is essential for model simulations of the EASM precipitation.