This study estimated sunshine duration in South Korea using cloud detection images; the 2 class and 5 class images of Communication, Ocean and Meteorological Satellite (COMS). The images were preprocessed and then compared with the observed sunshine duration from the Automated Synoptic Observing System (ASOS). Based on the result of comparing yearly and monthly sunshine duration, the results of the 5 class were better than the results of the 2 class. In the case of comparing daily sunshine duration, the results of the 5 class also showed relatively better outcome than the 2 class images. The simulation performance of the sunshine duration observed by ASOS and the sunshine duration calculated by COMS were evaluated using Kling-Gupta Efficiency (KGE) technique. The 5 class data showed relatively high efficiency. RMSEs were relatively lower in the 5 class than the 2 class image in all years (2011-2014). Therefore, the 5 class data among the COMS satellite images could provide meaningful information at the points where there is no observation of sunshine duration.