Arrays of single-crystalline Al doped ZnO rectangular nanorods were synthesized and nucleated from single-crystalline ZnO nanosheets by thermal chemical vapor deposition. The rectangular nanorods were grown from the periodic thicker regions of the nanosheets, associated with Al concentration fluctuation and evidenced from electron energy loss spectroscopy. High-resolution transmission electron microscopy also shows variations in the lattice constant and dislocations at the interface due to lattice strain. The composition modulation induced by doping may serve as a driving force for creating interesting nanostructures with tunable properties.