Exploring novel ammonia sensors operated at room temperature holds great promise for various applications. Herein, we synthesized p-type delafossite AgAlO2 nanoparticles via hydrothermal method. The nanoparticles show a single Ag-deficient 3R delafossite phase with particle size between 200 and 500 nm. The sensor based on AgAlO2 nanoparticles exhibits high sensitivity, fast response-recovery and good selectivity to 100 ppm ammonia at 293 K 20-70 %RH. More interestingly, the sensor shows a pseudo n-type response to ammonia at 293 K 35 %RH, but a p-type sensing behavior at elevated temperature of 573 K. The temperature-dependent pseudo n-type response to ammonia gas is ascribed to the competition of extrinsic and intrinsic sensing behaviors, which resulted from the reaction of ammonia gas with surface adsorbed water molecules and adsorbed oxygen ions, respectively. The former can regulate the conduction of the adsorbed water layer, which contributes to the total conductivity as an external part, while the latter can modulate the intrinsic conductivity of the sensor by changing the hole concentration of AgAlO2. This work might provide a new idea to design low temperature gas sensors. (C) 2018 Published by Elsevier B.V.