Long-term simulations of surface ozone (O3) over East Asia during 1980–2020 were conducted using the regional scale chemical transport model (CMAQ) and the newly developed year-by-year emission inventory in Asia (REAS). The CMAQ with the REAS could reproduce the spatial and seasonal variations of the observed surface O3 concentrations in 2000 and 2001. The historical simulation from 1980 to 2003 demonstrates that an annually-averaged concentration of surface O3 over the Central East China (CEC) and Japan increases about 12 ppbv (1% year-1) and 5 ppbv (0.4% year-1) during a quarter century, respectively. This simulated trend in Japan generally agrees with the observed trend measured at monitoring stations and is correlated with the trend of Chinese NOx and NMVOC emissions. The future emissions up to 2020 were projected based on three emission scenarios (PSC, REF, and PFC). In 2020, the Chinese NOx emissions in each scenario are expected to increase by - 1% (PSC), +40% (REF), and +128% (PFC) from 2000, respectively. The worst scenario (PFC) shows that the East Asian NOx emissions almost double between 2000 and 2020. We find that the surface O3 concentrations in East Asia will increase significantly in the near future due to projected increases in NOx emissions.