The research have been conducted for identifying the thickness of volcanic rock layer that prohibits the hydrocarbon potential in Majalengka District, Indonesia by using passive seismic method. The potential reservoir is expected on sedimentary rock of Cinambo Formation below the volcanic layer. The hydrocarbon potential are proven by the presence of oil seepage in the northern side of research area. Active sesimic survey showed unsatisfactory results because the volcanic layer has scaterred the seismic wave propagation. This study aims to strengthen the previous results and to determine the thickness of volcanic rock layer. Passive seismic is a method that can detect the thickness of layer by utilizing low frequency. Measurements carried out on an area of 15 km-square with acquisition time around 1 - 2 hours for each station. The equipment is a digital broadband seismometer with 3-axis components. The horizontal to vertical spectral ratio (H/V Spectral Ratio) showed that the natural frequency signal can correlate to the thickness of volcanic rock layer. The thickness of volcanic rock layer have been estimated using the Bard (2000) equation about the relation of natural frequency and the thickness of bedrock. A data inversion and 2D/3D modelling has been performed by using velocity model to show the thickness of volcanic rock layer through a velocity value. The results showed that the volcanic rock layer on the research area varies from 20 meters to 60 meters.