We report on the room-temperature hole-mediated ferromagnetism in Zn1-xMnxO thin films. Zn1-xMnxO (x = 0.03 and 0.20) films were prepared on GaAs (001) substrates by the rf magnetron cosputtering method. At the substrate temperature high enough to activate As diffusion from GaAs substrates, p-type Zn1-xMnxO films were synthesized. The superconducting quantum interference device (SQUID) and alternating gradient magnetometer (AGM) results clearly showed ferromagnetic characteristics at room temperature.