Ultra-thin porous ZnO nanosheets with high regularity were obtained by electrodeposition followed by annealing. The nanosheets were first electrodeposited by controlling the concentration of potassium acetate (KAc) in nitrate electrolyte. The effects of KAc concentration on the electrochemical behavior, the composition and morphology of samples were further discussed. It was indicated that the as-deposited nanosheets were a mixture of ZnO and zinc acetate hydroxide hydrate (ZAHH). After annealing at 450°C for 30min, ZnO/ZAHH nanosheets with smooth surfaces were converted to pure ZnO nanosheets with porous structure, which were oblong in shape, ultra-thin (about 20nm in thickness) and constructed with well-distributed single-layer ZnO nanoparticles with the size of 30–60nm. As preliminary application in quantum dots-sensitized solar cells (QDSCs), porous ZnO nanosheets were co-sensitized with CdS and CdSe QDs and the QDSCs based on porous ZnO nanosheets deposited for 15min achieved a high efficiency of 2.67%.