Achieving extremely high sensitivity is an important indicator in the development of novel and stable gas concentration sensors. In this paper, we present a gas concentration sensor with parity-time symmetry for high sensitivity at low concentrations. The proposed sensor can detect toxic gases, such as benzene, bromine, and acetone, by probing the faint changing of the permittivity. Furthermore, the level of the sensitivity can be adjusted by the resistance segment, which is realized by various metallic formations. Our proposed structure provides a novel idea for the development of future gas concentration sensors, showing an exciting prospect for gas sensing technologies.