Mn doped ZnO films with and without N codoping have been fabricated by oxidative annealing of sputtered Zn:Mn and Zn2N3:Mn films on silicon substrates in flowing O2 ambient. It was found that the ZnO:Mn films show very weak ferromagnetic behavior, while for those with N codoping, significant ferromagnetism with a moderate saturation magnetization of about 0.23—0.61 μB per Mn2+ ion was observed at room temperature. It suggests that significant ferromagnetism in ZnO:Mn films could be activated by N codoping. The results indicate that holes are favorable for ferromagnetic ordering of the doped Mn2+ ions in ZnO, in agreement with the recent theoretical studies.