The Kanmon Strait is located on one of the most important routes in Japan. The results of a traffic survey of its eastern half, the Hayatomo Strait, had been reported ; but there remained that in the western half, the Oseto. This needed the necessity of conducting a similar survey for the remaining half, to understand clearly the traffic conditions of the Kanmon Strait. The first four day radar survey with visual observation was conducted from Aug.21 to 25 of 1967 for Area B, and the second one from Aug.30 to Sept.3 for Area A. The results obtained are summarized as follows: 1. More than 800 vessels passed through the strait a day. 2. About a half of them was those smaller than 100 G.T. 3. About three quarters of them passed in the daytime and the rest at night. 4. The strong tidal current did not cause any remarkable decrease in the passing of the vessels. 5. One of the most admonitory findings was the passing of small boats across the lawful course. This suggested much risk of inducing collision. Namely, the vessels over 3, 000 G.T. passed along the fairway regardless of the relative direction and speed of the tidal current. In contrast with this, both of the easting and westing courses of the smaller boats than 100 G.T. converged into along the northern periphery in the Oseto, but diverged over the western waters adjacent to it.