This study examined the impact of foreign SO2 emission changes on the aerosol direct radiative effects (ADRE) in South Korea. Simulations that applied basic emissions (BASE) and simulations that applied reduced SO2 emissions from foreign sources (R_FSO2) were performed, respectively, using the Weather Research and Forecasting (WRF)-Community Multiscale Air Quality (CMAQ) two-way coupled model. In addition, the difference between the two experimental results was calculated (i.e., R_FSO2 minus BASE) to quantitatively identify the impact of foreign SO2 emission reduction. The reduction in foreign SO2 emissions caused a decrease in the concentration of SO2 flowing in from overseas to South Korea. As a result, a clear decrease in SO42− concentration was shown mainly in the southwest coast of South Korea. The difference in PM2.5 concentration in South Korea according to the foreign SO2 emission reduction did not correspond to the difference in SO42− concentration; it was determined in a complex way by the changes in SO42− concentration caused by SO2 concentration changes, and the subsequent series of changes in NO3− and NH4+ concentrations. The differences in SO42− and PM2.5 concentrations caused by the foreign SO2 reduction also affected the ADRE changes in South Korea. The distribution of ADRE difference between the two experiments was not consistent with the distribution of PM2.5 concentration difference, but it was very similar to the distribution of SO42− concentration difference. These results imply that the ADRE of South Korea is not simply proportional to PM2.5 concentration and may be determined by concentration changes of SO42−.