Petrology, geochemistry, formation environment and isotopic geochronology of Precambrian amphibolites in Alxa area are reported in this paper. Amphibolites in different group complexes, formation complexes and complex rock bodies all crop out in layers, and their protoliths are mainly ferrian tholeiite characterized geochemically by high potassium and titanium as well as rich REE and LREE. These characteristics are remarkably different from features of typical oceanic tholeiite, TH_1 and TH_2 tholeiite of Archean rock assemblages. Various geochemical diagrams indicate that amphibolites are mainly formed in an intraplate environment characterized by intraplate depression or epicontinental faulted depression. Isotopic geochronology shows that amphibolite in Diebusige group complex was formed in Neo_archean. ~(39)Ar_~(40)Ar age and isotopic age of hornblende from biotite_bearing amphibolite are 1?918 Ma and 1?919 Ma respectively, suggesting that they underwent metamorphism of amphibolite faces in Paleoproterozoic. Amphibolite in Bayanwulashan formation complex was formed between (2?271) Ma and 2?264 Ma. Amphibolite in Boluositanmiao gneiss complex was intruded by granitic gneiss of 1?818 Ma and 1?839 Ma. According to geochemical characteristics of amphibolite in the complex and the same sort of rocks in Bayanwulashan formation complex, it is concluded that it was formed in early Paleoproterozoic. Accurate isotopic chronological data of amphibolite from Delhetongte formation complex in Alxa Group are not available, but the average zircon ion probe age of garnet_muscovite_biotite_quartz_schist in the same layer is 1?363 Ma, which indicate that the amphibolite was probably formed in Meso_proterozoic.