By using ab initio density functional theory, effects of Mn doping on the electronic and magnetic properties of armchair and zigzag single walled ZnO nanotubes are investigated. For this purpose spin up and spin down electrons density of states, charge density topography, counter plot, magnetization, and polarization in terms of Mn are calculated. We found a half-metallic behavior for armchair ZnO nanotube while it is not observed for zigzag ZnO nanotube within generalized gradient approximation (GGA). Polarization of armchair has an oscillation while for zigzag it is saturated at higher Mn concentration. We observe a half-metallic behavior for Mn-doped (6,0) zigzag ZnO nanotube when going from the GGA to GGA+U.