Here we report a system using ultrathin SnO2 nanosheets with high reactive exposed (110) surface modified gold electrode for sensitive detection of As(III) by Square wave anodic stripping voltammetry (SWASV) with a mild acid condition (pH 5.0). Ultrathin SnO2 nanosheets have been synthesized via a hydrothermal process successfully with the thickness of about 0.52nm (four atomic layers thick). This oxide is used as electrode modifier, and the modified electrode exhibits good performance in stripping determination of As(III). The LOD actually measured is 5μgL−1 and below the guideline value given by the World Health Organization (WHO). As compared with SnO2 bulks, ultrathin SnO2 nanosheets are found to exhibit stronger adsorption capability and better detection performance toward As(III), it may be due to the atomic thickness and extremely huge percentage of (110) facet ultrathin nanosheets materials exposed. Finally, this system is successfully applied for the analysis of a real sample collected from Inner Mongolia, China. Most importantly, we pose a potential for the use of ultrathin materials to improve the electrochemical performance of bare gold electrode in mild acid condition.