The spin-coated films of 2,9,16,23-tetra(heptyloxy)phthalocyanine showed very good gas sensing properties to NO2 at room temperature. The response and recovery are rapid and complete with good reproducibility and high sensitivity. The magnitude of response of the film to NO2 are enhanced by irradiation with light. This may be ascribed to the decrease in the activation energy for the charge transfer interaction between the phthalocyanine donor and the gas acceptor by light excitation.