There are several ways to reduce the number of bolts of frictional bolted joints from the viewpoint of the construction cost and the maintenance cost for steel structures. For example, there are the ways which are strengthening the material of bolts, or increasing the slip coefficient. This study is focused on the slip coefficient with metal thermal sprayed contact surfaces. The objective of this study is to investigate the effects of different surface conditions on the slip coefficient. Therefore, slip tests were conducted in consideration of 9 patterns of surface treatment method (3 kinds of thickness, 3 kinds of material of sprayed metal).