The template-free synthesis of hierarchical m-ZrO2 nanorods by a simple hydrothermal method and its possible formation mechanism based on a series of chemical reactions have been proposed here. The traditional preparation methods of hierarchical ZrO2 nanorods are involved in expensive equipment, complicated process and high production cost. Owing to their physical and chemical properties hierarchical ZrO2 nanorods have received considerable attention. The results revealed that as synthesized products are composed of many nanorods with 100-200 nm in diameter and 3-5 mu m in length. The final product after annealing is involved into hierarchical monoclinic ZrO2 (m-ZrO2) nanorods, the big nanorod was made up of many small nanorods with 30-40 nm in diameter and 350-450 nm in length. This discovery could open a new path to the template-free synthesis of hierarchical nanomaterials. (C) 2014 Elsevier B.V. All rights reserved.