Theory has predicted that high temperature ferromagnetism (FM) should be found in cubic Mn-doped ZrO 2. Our experimental data reveal room temperature FM in Mn-doped ZrO 2 thin films grown on LaAlO 3 substrates. The largest saturated magnetic moment (M s) is found to be about 13.8 μ BMn for the cubic Mn 0.05Zr 0.95O 2 films and it decreases as the Mn content increases. In this case, the intrinsic FM is strongly associated with the cubic structure of Mn-doped ZrO 2, and the Mn-Mn exchange interactions via intermediate oxygen atoms is important. Room temperature FM is also observed in monoclinic Mn-doped ZrO 2 thin films grown on Yttrium Stabilized Zirconia (YSZ) substrates, however, with a completely different nature. Though pristine monoclinic ZrO 2 films are already ferromagnetic, doping Mn can enhance the magnetic moment by about 40 (M s is 2.68 μ BMn). Differently from the cubic case, FM in monoclinic Mn-doped ZrO 2 films does not come only via exchange interactions, but also from defects. © 2012 American Institute of Physics.