A series of transitional mafic—ultramafic rocks related to both copper—nickel sulfide and vanadium—titanium magnetite occurred in the Eastern Tianshan Mountains, such as the Xiangshanxi, the Niumaoquan, Tudunnan (Er’hongwa) and Hongliangzi mafic—ultramafic rocks. With zircon U Pb and amphibole 40Ar/39Ar thermochronology method, the ages of the Niumaoquan, the Er’hongwa and the Hongliangzi mafic—ultramafic rocks can be obtained. The results show that the Niumaoquan mafic—ultramafic rock emplaced at the age of 289.7±2.4 Ma, Er’hongwa rock at 274.2±5.7 Ma and Hongliangzi rock at 309.7±1.5 Ma. In addition, the major elements, trace elements, REE and Sr—Nd isotopic compositons of these mafic—ultramafic rocks are analysed. The results show that these rocks are composed of both alkaline series, calc alkaline series and tholeiitic series rocks. The ratios of magnesium and iron (m/f) is from 0.44 to 4.76, which belongs to ferro basic rocks series. The compositions and parameters of MgO, FeO, CaO, (Na2O+K2O), TiO2 and SiO2 show that these mafic—ultramafic rocks have features of both related to V—Ti—magnitite deposit and Cu—Ni sulphide deposit or have transitional features of them. REE fractionation and model curve changed clearly. LREE/ HREE ranges from 1.39 to 5.47, and ［n(La)/n(Yb)］N ranges from 0.79 to 4.65 and they varied clearly. In addition, δEu anomaly changes from 0.85 to 2.33. Enrichment between primitive mantle normalized large ion lithophile elements and high field strength elements is not obvious, but overall samples generally have depleted with Th, Ta, Nb, Ti and enriched with Sr and Ba. The vast majority of the value of εNd(t) is positive, and ［n(87Sr)/n(86Sr)］i values are generally lower, which indicated that this type of rock source area is the depleted lithospheric mantle, and experienced a strong differentiation.