Under the generalized gradient approximation (GGA), the electronic and magnetic properties of armchair SiC/AlN nanoribbons have been investigated by using the first-principles projector-augmented wave (PAW) potential within the density function theory (DFT) framework. The unpassivated SiC but not AlN edge can cause magnetic moments of the nanoribbons. The net up-spin charge mainly accumulates at C1, C2 and Si1 sites for ferromagnetic nanoribbons. The increasing concentration of Si–C chains has little effect on the magnetic properties of the nanoribbon, whereas the number of the dangling bonds caused by Si and C atoms strongly affects the magnetic of the system.