MnO2 with different morphologies was controllably synthesized. The co-effect of some anions (SO42-, NO3-, PO43- and Cl-) and pH on the hydrothermal crystallization of MnO2 was also investigated systematically. The final products were characterized by XRD, TEM and SEM. Based on our experimental results, we propose that the coarsening of MnO2 can be impeded by anions. While when pH is dominant, this dissolution procedure can be accelerated and MnO2 nanorod formed through dissolution-recrystallization process. The present work may provide a new sight into the anisotropic growth of MnO2. (c) 2012 Elsevier Ltd. All rights reserved.