Resistivity-based high-density prospecting methods have recently increased to be applied to tunnel, landslide and other ground investigations. Therefore, it is essential to establish the rock classification technique by resistivity-based high-density prospecting data. In this paper, the authors try to propose a tunnel rock classification technique, in which the converted seismic wave velocity based on resistivity-based high-density prospecting data can be used for classifying tunnel rock mass. Furthermore, the applicability of the proposed tunnel rock classification technique is discussed, by comparing estimated support patterns with actually performed ones.