We have produced a variety of 2D nanosheets by exfoliating layered transition metal oxides into colloidal single layers.[1,2] Osmotic swelling induced by reaction with aqueous amine solutions to homogeneously prop the interlayer gallery up to a hundred times is a key step for high-yield production of unilamellar nanosheets.[3,4] The resulting 2D oxide crystals have a molecularly thin morphology, which is similar to graphene.On the other hand, these nanosheets are characterized by their rich varieties in composition and structure, which leads to a range of functionalities.For example, Ti or Nb oxide nanosheets of Ti1-dO24-and Ca2Nb3O10-work as wide-gap semiconductors, showing photocatalytic property, while Mn-or W-based oxide nanosheets such as MnO20.4-and Cs2W11O352-show redox activity and chromic property.