Electrical conductivity and thermal degradation studies of phenothiazine (PTZ), acetophenzazine dimaleate (APM), methdilazine hydrochloride (MDH) and mepazine hydrochloride monohydrate (MH) are reported. The activation energies are evaluated based on their electrical conductivity study conducted over the temperature range 30-150 degrees C. These energies for PTZ, APM, MDH and MH are found to be 0.44, 0.41, 0.34 and 0.47 eV, respectively. MH showed unusual temperature dependence metallic and semiconducting electrical conductivity. The parent compound and other derivatives showed semiconducting behaviors. The materials are analyzed for the kinetic parameters like the activation energies for decomposition and the Arrhenius pre-exponential factors in their pyrolysis region using Broido's, Coats-Redfern and Horowitz-Metzger methods. Using these factors and the standard equations thermodynamic parameters such as enthalpy, entropy and free energies are calculated. Thermogravimetric study on these phenothiazine derivatives in air indicated that their stabilities are in the order APM > MDH > PTZ > MH. (C) 2007 Elsevier B.V. All rights reserved.