An ac impedance method has been used to study the electrical properties of an illuminated HgI//2 crystal as a function of temperature left bracket 10-350 K right bracket and frequency left bracket 1-10**4 Hz right bracket . The complex impedance plane plots enabled us to determine the bulk resistance of the crystal as a function of temperature. Activation energies of left bracket 0. 08 plus or minus 0. 005 ev right bracket and left bracket 0. 25 plus or minus 0. 01 ev right bracket are then found; they are attributed to acceptor and donor trapping levels, respectively. At temperatures lower than 230 K, a weak temperature dependence of the bulk resistance is observed. This weak dependence is supposed to be due to photoconductivity. This study is relevant to the potential of HgI//2 as a radiation detector.