Flowerlike ZnO nanostructures (FZNs) have been deposited on Si substrate from aqueous solution by the hexamethylenetetramine (HMT)-assisted thermolysis of zinc-ethylenediamine (en) complex at low temperature (95 degreesC) and in a short time (60 min). Obtained FZNs exhibit well-defined flowerlike morphology, hexagonal wurtzite structure, and strong UV photoluminescence. The flower petals constructed by many well-aligned nanorods possess the typical tapering feature with tip sizes of 30-50 nm. Effects of en. zinc-en molar ratio. HMT, and reaction time were investigated. Results show that en is determinative to the formation of FZNs, and the partial capping of NH3.(CH2)(2)(NH3)-N-. molecules on the side surface of the ZnO crystal is responsible for the tapering feature of petals. HMT can step into the nucleation process of ZnO and inhibit the formation of nanorods on the substrate by preventing heterogeneous precipitation. Moreover. the formation of twin crystal ZnO nuclei at low precursor concentrations and their further evolution into spindle crystals with clear middle interfaces are also vitally important for the development of FZNs.