α-Hydroxyl fatty acids (α-HFA) were hydrothermally synthesized through neutral hydrolysis of α-chloro fatty acids (α-CFA) derived directly from natural fatty acids, which is a novel green route to synthesize α-HFA from natural fatty acids with the characteristics of high yield, low-cost and environmental-friendly. In this paper, the structure of α-HFA was identified by FTIR and GC-MS and the relative molecular weight was confirmed by ESI-MS. The purity of purified α-HFA as 99% was examined by GC. Moreover, the influence of mass ratios, water dosages, reaction temperatures and reaction time on the hydrothermal synthesis has been studied. The results indicate that the yield of α-hydroxyl natural fatty acid (C12~C18) can reach 98%~99% under the following conditions: n(CaCO3) : n(α-CFA) = 1.05 : 1; m(H2O) : m(α-CFA) = 2 : 1 at 155 oC for 4 hours.