A bright white light-emitting material based on CdSe QDs was prepared by a facile post-synthetic treatment of passivating the QDs by hyperbranched polyethyleneimine (PEI) in water. The CdSe@PEI aqueous solution emits white light with CIE coordinates (0.334, 0.347) and a PLQY of (17.7 ± 0.1)%.