In this study, two flower-like delta-MnO2 microflowers and alpha-MnO2 nanotubes were synthesized by a simple hydrothermal route. The catalytic activities of three samples for resorcinol degradation and oxidation of formaldehyde (HCHO) were evaluated, and the effects of crystal phase and morphologies on the activities of the three MnO2 samples were investigated. The activities of the catalysts decreased in the order of alpha-MnO2 nanotubes > two of delta-MnO2 microflowers and alpha-MnO2 nano-tubes degraded resorcinol in 30 min at resorcinol concentration 20 mg L-1 and achieved complete HCHO conversion at 80 degrees C. It was found that the crystal phase and morphologies of the MnO2 samples mainly predominated the catalytic activities.