Irreversible electroporation (IRE) is attracting attention as a new technique to treat tumors, in which electric pulses over a certain threshold perforate the cell membrane and induce necrotic cell death. Since the electric pulses potentially generate the Joule heating around electrodes, successful IRE needs to apply a pulsed voltage high enough for the irreversible perforation yet minimizes the thermal effect on the extracellular matrix in the surrounding tissue. The temperature rise around the electrodes is therefore one of the most important concerns in the IRE. However, no experimental evidence has been reported for the temperature rise because of extremely short pulses used in the IRE. The aim of this study was therefore to establish a new method to detect the temperature rise during the IRE. A key technique is to use temperature-sensitive ink to visualize in situ instantaneous temperature rise. Chromatic change of the ink that depends on the temperature was preliminarily calibrated by a transient short-hot-wire technique combined with color analysis of the ink, and then utilized to determine the temperature distribution after electroporation. The maximum temperature rise was thus successfully visualized after the electroporation using agar gel as a tissue phantom. Our method is useful for direct evaluation of a risk of thermal damage and provides experimental evidence for theoretical study. (C) 2012 Elsevier Ltd. All rights reserved.