Periodic characters of water temperature in the regions of the Mishima and the Okinoshima were derived through the analysis of the five days interval data during 1914 to 1970 mainly. In terms of ten days mean temperatures, annual variation function of the Mishima region, Korea Strait, is F($ heta_d$)=17.45-5.34 cos $ heta_d$-3.77 sin $ heta_d$+0.62 sin $2 heta_d$ -0.52 sin $3 heta_d$, where $ heta_d$=$frac{pi}{18}$(d-2), d is the order of ten days period 1 to 36. And in the region of Okinoshima, Tsushima Strait, we find F($ heta_d$)=18.88-5.39 cos $ heta_d$-3.60 sin $ heta_d$+0.52 sin $2 heta_d$. The annual mean temperature is 17.4$^{circ}C$ in the Mishima region, 18.9$^{circ}C$ in the Okinoshima region, and the amplitudes of annual variation functions are 7$^{circ}C$ in both regions with minimum temperature in the middle ten days of February, maximum in the middle ten days of August. The long term variations of surface water temperature with 12 5 years period were observed in the annual mean temperature, monthly mean temperatures and the fixed day temperatures of every year. In addition to these, relatively short term variations were also found significant periods of 3 years, 4 years and 2 years, respectively.