The craving for controllable assembly of geometrical nanostructures from artificial building motifs, which is routinely achieved in naturally occurring systems, has been a perpetual and outstanding challenge in the field of chemistry and materials science. In particular, the assembly of nanostructures with different geometries and controllable dimensions is crucial for their functionalities and is usually achieved with distinct assembling subunits via convoluted assembly strategies. Herein, we report that with the same building subunits of α-cyclodextrin (α-CD)/block copolymer inclusion complex (IC), geometrical nanoplatelets with hexagonal, square, and circular shapes could be produced by simply controlling the solvent conditions via one-step assembly procedure, driven by the crystallization of IC. Interestingly, these nanoplatelets with different shapes shared the same crystalline lattice and could therefore be interconverted to each other by merely tuning the solvent compositions. Moreover, the dimensions of these platelets could be decently controlled by tuning the overall concentrations.