Lead phthalocyanine (PbPc) films containing 93.0 wt.% PbPc were deposited by spin coating technique using polypyrrole (PPy) as a binder. The film response toward nitrogen dioxide (NO 2) was found to be a first-order reaction. The rate-determining step was the charge transfer between the adsorbed NO 2 and the film surface. The activation energy for the first cycle of exposure (14.3 kJ mol −1) was found to be higher than that for the second cycle (13.0 kJ mol −1), corresponding to the higher rate constant for the second cycle. The NO 2 response of the film was found to obey the Elovich equation and thus NO 2 concentration can be derived from rate of reaction.