Several α-MnO 2 catalysts in the forms of nanosphere, nanorod and nanowire were synthesized, characterized and tested in heterogeneous activation of peroxymonosulfate for phenol degradation in aqueous solutions. The α-MnO 2 materials exhibited varying activities in activation of peroxymonosulfate to produce sulfate radicals for phenol degradation depending on structure and morphology. Crystalline structure of MnO 2 is more important than porous structure in influencing the activity because crystalline α-MnO 2 exhibited higher phenol degradation. Nanowired α-MnO 2 presented the highest activity with stable performance while the mesoporous α-MnO 2 nanosphere with amorphous structure presented the lowest activity and stability. Kinetic study showed that phenol degradation on α-MnO 2 followed the first order kinetics.