|The groundwater seepage in a tunnel is considered as one of serious causes of deformation and deterioration of lining concrete and other materials in the tunnel (MLIT, 2014; JRA, 2015). Therefore, it is very important to grasp the groundwater distribution around the tunnel for designing effective countermeasures. In this study, P-wave velocity by the seismic refraction and electric resistivity by the electric surveys in a tunnel are used for estimating porosity and water content to delineate the groundwater distribution in the rock surrounding the tunnel. This estimation is performed with the transform analysis proposed by Kusumi et al. (2006) based on the empirical equations by Wyllie et al. (1956) for P-wave velocity and Archie (1942) for electric resistivity. In this study, the empirical equation for P-wave velocity by Raymer et al. (1980) is also used to make the estimation more accurate. The estimated porosity and water content profiles are verified through comparison with actual observations of tunnel wall deformations and ground water seepages.