In this study, long-term variability in the coastal sea surface temperature (SST) in Korea was investigated to examine the earlier results in depth by analyzing the coastal SST time series extending to recent years. Spectral analysis shows not only dominant peak of annual period as expected but also evident peak of semi-annual period at most of the stations with 4-month period at some stations. It is shown that interannual variability has a common tendency at most of the stations with some differences between eastern and western coast. Long term increasing trend is remarkable at almost all the stations with the rate over 0.02°C/year. The increasing trend of minimum SST in winter is obvious at most stations and the increasing rate is larger at the stations in the eastern coast, but the linear trend of maximum SST in summer is less definite. Therefore, the decreasing tendency of annual amplitude is mainly due to the increasing tendency of SST in winter.