Effects of surface treatment of titanium on hydrogen absorption were investigated. Surface-treated titanium specimens prepared by polishing, anodizing, and air oxidizing were immersed in 0.5 to 6 percent hydrochloric acid (HCl) solutions at a temperature range of 70 to 250°C. After immersion, the weight loss, hydrogen content, and oxide film thickness of three specimens were measured. As a result, it became clear that anodizing did not reduce hydrogen absorption of titanium because the titanium oxide film formed by anodizing had dissolved after a short period in dilute HCl solution; however, the air-oxidized specimen was stable in this solution for a long time, and therefore hydrogen absorption of titanium was prevented. These laboratory test results correspond to the results of field tests conducted in hot molten urea and mineral acid solution at high temperatures.