Electrical and gas sensing properties polyaniline-chloroaluminium phthalocyanine (PAni-ClAlPc) composite thin films were investigated to study the gas sensing behavior of composites. Devices (chemiresistor gas sensors) were prepared by spin coating method from PAni as the base of composites and ClAlPc (with different concentrations) as the second component onto interdigitated electrodes. The sensitivity, reversibility, response and recovery time of these thin films on exposure to different concentrations (0–2000 ppm) of CO2 gas and the suitability of different composites as materials to be used in practical gas sensors at different temperatures were investigated. The sensitivity factor of composites was obtained in a range between 0.05–7.20. PAni + 10% ClAlPc was the perfect candidate composite to fabricate gas sensor at 300 K and PAni + 15% ClAlPc at 350 K. Thus, (PAni-ClAlPc) composites have better response than pure PAni. After that, devices were exposed to humidity, an unexpected behavior was absorbed. Conductivity of thin films were increased on exposure lower RH% and decreased on higher RH%. Finally, 1000 ppm CO2 was mixed to humidity and introduced to chamber, obtained results showed the CO2 mixtures decreased the sensitivity of thin films in compare with pure CO2.