We reported the preparation of uniform square nanosheets with tunable size by the living crystallization-driven 2D self-assembly of hyper-branched poly(ether amine) capped with heptaisobutyl polyhedral oligomeric silsesquioxane (POSS). The nanosheets of HP1 containing both anthracene (AN) and POSS moieties in a solution of 1,4-dioxane and water can be fragmented after the melting of the PUSS moieties upon heating and can be regenerated after the recrystallization of POSS moieties, which was confirmed by microdifferential scanning calorimetry (mu DSC) and dynamic light scattering (DLS) studies and transmission electron microscopy (TEM) images. The obtained fragmented nanosheets (HP1-NSs) with a relatively small size were used as seeds for the 2D epitaxial living growth of HP1 unimers to fabricate uniform square nanosheets with tunable edge lengths from similar to 0.5 to similar to 4.5 mu m, which is dependent on the unimer-to-seed ratio. Furthermore, dual-component nanosheets can also be obtained by random cocrystallization of HP1 with another type of hPEA capped with POSS and ferrocene (HP2). This crystallization-driven 2D self-assembly behavior of POSS-capped hPEA might provide potential significance in the preparation of functional nanosheets with different sizes and components, which could be further used as templates for inorganic nanosheets and 2D-platforms for metal nanoparticles.