The surface properties of monoacyl trehaloses with different acyl chains were investigated at 30°C, 40°C, 50°C, and 60°C. Monoacyl trehaloses were enzymatically synthesized and purified with silica gel column chromatography and semi-preparative high-performance liquid chromatography (HPLC), and the purity of products was identified by mass spectrometry (MS) and nuclear magnetic resonance (NMR). The surface tension of monoacyl trehalose in pure water was measured using Doüy ring method at different temperatures. The critical micelle concentrations (CMC), surface tension at the CMC, , and residual area per molecule, , were estimated from the curves. The CMC value of unsaturated monoacyl trehalose was affected by both the degree of unsaturation and the acyl chain length, and the effect of chain length on the CMC value was much stronger than that of the unsaturation degree. However, there was no significant dependency of the value and a values on the chain length or the unsaturated degree.