Owing to the unique thickness dependent physical and chemical properties, two-dimensional (2D) layered nanomaterials have received tremendous attention and shown great potential in fabrication of high-performance electronic/optoelectronic devices. Notably, the implication of 2D nanomaterials in gas-sensing field has also drawn considerable attention but few related review works have been reported. This critical review mainly focuses on the current progress of 2D layered nanomaterials in gas-sensing applications. Firstly, we describe the basic attribute of 2D layered nanostructures and discuss the fundamentals of their gas-sensing applications. Secondly, we have numerated recent gas-sensing works on typical 2D layered nanomaterials , including graphene, MoS2, MoSe2, WS2, SnS2, black phosphorus, and the others . Particularly, the optimized strategies for improving their gas-sensing performances are also discussed here. Finally, we conclude this review with some perspectives and outlook on future advances in this field.