Developing of novel chemiresistive gas sensing materials with desired unique gas chemisorption properties is of great important. In this work, motivated by the special electronic structure, Ag3PO4 semiconductor is systematically investigated as gas sensing material for the first time. Encouragingly, the Ag3PO4 nanoparticles based gas sensors exhibit high selectivity to NH3 at near room temperature of 50 degrees C with negligible responses to the other gases (including H-2, CO, ethanol, acetone, NO2 and SO2). Furthermore, the responses decreased with the increase of operating temperature from 50 to 100 degrees C, indicating the superior NH3 sensing activity. The in-situ infrared characterization and theoretical calculations reveal that the lone pair of NH3 coordinate with the superficial silver atoms of Ag3PO4 accompanied with strong adsorption energy, efficient quantities electron migration and thermodynamic favorable, explained the origin of the high selectivity. Our work indicates that Ag3PO4 based materials are very promising low operating temperature and highly selective NH3-sensing materials.