Sifangtai complex is the largest mafic-ultramafic intrusion along the Shangdan fault in the North Qinling orogenic belt, covering an area of ～40 km². It consists mainly of ultramafites, pyroxenite and minor intermediate rocks, intruding into the Danfeng Group. A combined study of cathodoluminescence images (CL) and in situ LA-ICP-MS U-Pb isotope dating was carried out for zircons from the Sifangtai gabbro. Cathodoluminescence images show two kinds of zircon grains, i.e., prismatic ones with clear magmatic zonations and round ones with complicated internal structure, some of the latter ones having no magmatic zonation. Altogether 32 U-Pb analyses were made for cores and overgrowths of 26 zircon grains,and the magmatic age 460±29 Ma of Sifangtai mafic-ultramafic complex was obtained. The 32 data can be divided into 4 phases: 400～500 Ma, 700～900 Ma, 1 800～2 600 Ma and 2 700～2 918 Ma. The result of 400～500 Ma is consistent with the Caledonian movement in the Qinling orogenic belt, while the result of 700～900 Ma is probably related to the mantle superplume that broke up Rodinia in mid dle and west China during 830～740 Ma.