In this study are observed and anlayzed the corrosion phenomena in leak site and the effect on temperature at the target surface of heat transfer tube material by sodium-water reaction through small water leakage in liquid sodium atmosphere. Surrounding of leak hole of the specimen was damaged by the wastage phenomena due to corrosion and erosion of material, and the damage at the leak site was extended from 150 μm to about 200 μm. Also, the size appeared in the target surface observed to about 1000 μm diameter. The temperature of target surface increased about 70 ~ 80 ℃ by heat of sodium-water reaction in spite of the small leakage in 15 ㎖ of water. Also, from the results of EPMa and EDX analyses, damaged area are covered with complex compounds such as (NaOH+Na₂O)·Fe_xO_y or (NaCrO₂+Na₂CrO₄) which mixed up with the sodium oxides formed by sodium-water reaction and the Fe or Cr element composed of matrix in target material.