The seismic refraction survey was conducted in the southwestern part of the Tokyo Metropolitan area to make clear the deep sedimentary structure. Two explosions were made at Daikoku and Maioka in Yokohama city in 1988, and the resultant seismic waves were observed at 83 temporary observation sites along four surveying lines:a) Yumenoshima to Enoshima, b) Daikoku to Nagatsuta, c) Nagatsuta to Kanazawa, andd) around Takatsu.The travel time analysis for the above data and additional data from previous explosions in the area for reference has been made.The followings were our conclusions:1) The subsurface structure consists of five layers characterized by P-wave velocities of 1.8, 2.3, 2.9, 4.7 and 5.5km/s. The top layer with a P-wave velocity of 1.8km/s disappears around Enoshima. The layer with a P-wave velocity of 5.5km/s could not be confirmed for the southwestward area.2) The topography of the layer with a P-wave velocity of 4.7km/s forms a synclined structure having its maximum depth of more than 4km between the Maioka and Daikoku explosion sites. The depth to this layer becomes drastically shallower toward Enoshima.3) The step-like topography of the layer with a P-wave velocity of 5.5km/s, which has been found in the previous study, could not be confirmed, because of low S/N ratios of the observed seismograms.