The mechanisms of polarization in chloranil pellets have been investigated by thermally stimulated discharge and ac dielectric measurements. Polarization was found to be mainly due to trapping of charge carriers at molecular sites and grain boundaries. A small dipolar contribution was also observed. Release of charges from molecular sites and dipolar reorientation occurred at about 120 °C with activation energy 0.8 eV. Charges from grain boundaries were released at a higher temperature (about 158 °C). Activation energy was calculated to be 1.06 eV.