When the electrolysis of 0.5 M D2SO4‐D2O solution was carried out using Pd or palladized Pd as a cathode material and Pt as an anode material, the emission of neutrons was detected by means of the fission track method and the production of tritium was investigated with a liquid scintillation method and a TPD using a mass spectrometer. The emission rate of neutrons was in the same orders of magnitude as the neutron flux in the background (10−3s−1). Otherwise, the existence of tritium in the cathode material after the electrolysis was identified by the measurement of the &bgr;‐ray emission when the specimens were immersed in the liquid scintillator. Moreover, mass peaks of m/z=5 and 6 which were considered due to DT as well as T2were identified in TPD, through the resolution of the mass spectrometer was not so high. The tritium production rate estimated by the &bgr;‐ray emission measurement was size orders of magnitude larger than the neutron emission rate. The difference betweeen them are briefly discussed.