This paper describes on the accuracy assessment for the Mobile Mapping System (MMS) point clouds and its practical experiments. In recent years 3D measurement technologies have advanced significantly. Especially, MMS has been becoming to be common as one of 3D measurement instruments. We have to consider the effective accuracy assessment method stands on the measurement mechanism of MMS point cloud. For these backgrounds, we propose the accuracy assessment by applying the Least Squares 3D (LS3D) surface matching method. Our accuracy assessment consists of “1)Data quality assessment, 2)Precision accuracy assessment, 3)Absolute accuracy assessment and 4)Relative accuracy assessment”. In order to examine our accuracy assessment, we had conducted an actual MMS run at Minato-Mirai, Yokohama, Japan. Through the practical experiments and actual evaluation, we confirmed that our proposed method is the effective for the MMS point cloud accuracy assessment. As future works, we have a plan to compare with terrestrial laser point clouds as the cross-sensor accuracy assessment.