Membrane-based gas separation is one of the critical technologies in filtration and separation industry, since it is more efficient, energy-saving and environmentally friendly compared with traditional separation technologies. Novel inorganic two-dimensional materials (2DMs) for gas separation are expected to achieve both high selectivity and high permeability, breaking through the trade-off between selectivity and permeability of commercial polymer membranes. This review begins with a brief explanation of gas separation mechanisms for membranes. Afterwards, special attention will be given to the recent advances in novel inorganic 2DMs including graphene and their derivatives, TMDs and MXene, about their design, fabrication and application in gas separation. The gas separation characteristics of different materials, their challenges and directions for future research are summarized. Moreover, the application of other novel inorganic 2DMs, such as LDH, h-BN and mica nanosheets in gas separation technology is also discussed. Finally, the perspectives and challenges for future research of novel inorganic 2DMs in gas separation field are outlined.