The electronic properties of AlN/SiC hetero-interface were investigated by using Al/AlN/4H-SiC MIS capacitors. Single crystalline AlN was grown on n-type 8degrees off-axis 4H-SiC (0001) epilayers via plasma-assisted molecular-beam epitaxy (PA-MBE). The C-V characteristics revealed that the initial pre-irradiation of atomic nitrogen (N*) before AlN growth strongly affected the electronic properties of AlN/SiC interface, which probably attributed to the atomic arrangement of Al, N, Si and C at the interface. A noticeably small value of interface state density (D-it), such as 3x10(11) cm(-2.)eV(-1) at E-c-0.2 eV, was obtained for the N* pre-irradiated interface.