This study developed a NH3 emission factor for bituminous coal power plants in South Korea in order to investigate the NH3 emission characteristics. The NH3 concentration analysis results showed that emissions from the selected bituminous coal power plants were in the range of 0.21–0.99 ppm, and that the difference in NH3 concentration was affected by NOx concentration. The NH3 emission factor was found to be 0.0029 kg NH3/ton, which demonstrated that the difference in the values obtained from the research conducted in South Korea was lower than the difference in the emission factor provided by the U.S. EPA, which is currently applied in the statistics of South Korea. NH3 emissions were compared by using the NH3 emission factor developed in this study alongside the EPA’s NH3 emission factor that is currently applied in South Korea’s statistics; the difference was found to be 206 NH3 ton/year. This implies that an emission factor that reflects the national characteristics of South Korea needs to be developed. The uncertainty range of the NH3 emission factor developed in this study was between −6.9% and +10.34% at a 95% confidence level.