We present the structural, electrical and magnetic properties in the (Al,Mn)N thin films with various Mn concentrations grown by plasma-enhanced molecular beam epitaxy. The X-ray diffraction patterns reveal that the (Al,Mn)N films have the wurtzite structure without secondary phases. The (Al1-xMnx)N films with x = 1.7% and 2.6% were obviously found to exhibit the ferromagnetic ordering with Curie temperature exceeding room temperature while the film with x = 3.0% was observed to show the ferromagnetic ordering at 5 K, indicating that a critical Mn concentration exists. Since all the films exhibit insulating characteristics, the origin of ferromagnetism in (Al,Mn)N might be attributed to indirect exchange interaction caused by virtual electron excitations from Mn acceptor level to the valence band within the samples. (C) 2004 Elsevier B.V. All rights reserved.