This review focuses on newly emerging two-dimensional MXenes for gas sensing applications from a theoretical to an experimental view to guide future research. Various synthesis routes of 2D MXenes have been explored and recent success of various MXenes has allowed more knowledge on the relations between their structure and materials properties. We review distinctive gas sensing properties of MXenes in two aspects of theoretical and experimental view. Theoretical insight into the gas-surface interaction mechanism and experimental results of various MXenes on their sensing properties are complied and discussed. To tailor and enhance the sensing performance of MXenes, the parameters such as precursors, morphology, surface terminations, and interlayer structures are emphasized. Perspectives on challenges and opportunities are offered for further development of MXenes-based gas sensors.