gamma-MnOOH nanorods with different diameters were synthesized by a simple one-step polymer-assisted hydrothermal method using 50% (wt.%) Mn(NO3)(2) solution and PEG-10000 as reagents. The diameters of as-synthesized gamma-MnOOH nanorods were well controlled by simply varying the volume of the 50% Mn(NO3)(2) solution. The calcination behavior of the as-synthesized gamma-MnOOH nanorods was studied. Nanorods of beta-MnO2 and alpha-Mn2O3 were synthesized by calcination at 350 and 600 degrees C for 1 h respectively.