To mitigate carbon emission from the combustion of fossil fuels, membrane is advantageous due to the fact that membrane is a thin interphase acting as a selective barrier separating two phases. This thinness, typically in the range of 100 nm to a few micrometers, provides an almost natural platform to implement functional nanostructures. In this review, the recent progress in nanostructured membrane materials for CO₂ capture will be discussed, including applications in flue gas decarbonizing (CO₂/N₂ separation) and syngas purification (CO₂/H₂ separation). In addition, the fundamentals of membrane technologies are also introduced. The reviewed nanostructure formation is confined to solid state materials, including polymer with intrinsic microporosity, carbon-based membranes, zeolite, and metal organic framework.