As the number of remaining shallow geothermal reserviors diminishes through exploitation, the geothermal industry must turn its efforts towards the detection and delineation of deep-seated geothermal resources. As a part of NEDO project, a extensive tensor magnetotelluric (MT) survey was carried out over the Kakkonda geothermal field in 1998. Seventy-six sites were arranged in four profiles to cross major structural features. To curtail spatial aliasing, the electric dipoles along each profile were deployed contiguously. The resistivity model within the area was derived using 3-D inversion. The upper 200-300m of the inversion result is of relatively low resistivity, corresponding to the Tertiary formation. Such resistivities are consistent with hydrothermal clay-rich sediments. Along the river of Kakkonda-gawa, there appear resistive zones with 100 ohm-m, which may be regarded as the Kakkonda garanite.