This paper describes on an accuracy investigation of point clouds which generated by MMS (Mobile Mapping System). In recent years 3D measurement technologies have advanced significantly. At the same time, MMS have become common measurement instruments for 3D application fields such as road facility management and related fields. We have to consider that the necessity of establishment positional accuracy evaluation methodology stands on the measurement mechanism of MMS point clouds. The aim of this study is to establish positional accuracy evaluation methodology for MMS point cloud measurement data and examine our LS3D (Least Squares 3D Surface matching) approach in practical experiments. Our proposed evaluation methodology consists of (1) Data Quality Assessment, (2) Precision Assessment, (3) Absolute Accuracy Assessment, (4) Relative Assessment, (5) Cross-sensor Accuracy Assessment. In order to examine our evaluation methodology, we had been carried out an actual MMS run and MMS point clouds generation at Minato-Mirai, Yokohama. Through our practical experiments and an actual evaluation, we confirmed that our proposed positional accuracy evaluation methodology is good enough procedures. As farther works, we have to accumulate much more evaluations than this moment.