Al2O3 mixed polyaniline composite with different dopant concentrations have been synthesized successfully by chemical oxidation method. X-ray diffraction, Fourier transform infrared spectroscopy, and UV-visible spectroscopy confirm the synthesis of the polyaniline and Al2O3 mixed polyaniline composite. Scanning electron microscopy shows the weak crystalline quality of the samples. The samples are found sensitive to ammonia gas. The sensing properties have been studied at different temperatures i.e. 25 degrees C, 50 degrees C, and 100 degrees C by varying the ammonia concentration over a range of 100-1500 ppm. The sensitivity increases with increasing Al2O3 concentration, increasing ammonia concentration, and also with increasing the sensing temperature. Sensitivity of these samples to ammonia gas is good with fast response. (c) 2013 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 130: 1941-1948, 2013