Abstract: The field geological survey and petrology study of the ultrabasic rocks in the Yizhuxingla area of the eastern Bangonghu-Nujiang suture zone show that the rocks in this area are strongly serpentinized peridotite.Geochemical studies show that these rocks are rich in MgO (45.33%~47.70%), poor in CaO (0.15%~0.37%) and Al₂O₃ (0.08%~0.39%), and deficient in TiO₂ (0.011%~0.014%).Its total content of REE is lower than that in the primitive mantle, and the REE distribution pattern is gentle to the right, the fractionation of light and heavy REE is obvious, and there are obvious positive Eu anomaly and weak negative Ce anomaly.Transition metal elements show an asymmetric W-type distribution pattern, forming obvious negative Ti and Cu anomalies, and the rocks have high (⁸⁷Sr/⁸⁶Sr)_i and low ε_Nd(t) characteristics.The above characteristics indicate that the ultrabasic rocks in the Yizhuxingla area is similar to SSZ type mantle peridotite.The depleted mantle rocks resulted form the partial meltingof original mantle(15%~25%).These ultrabasic rocks were formed in the oceanic island arc environment and had mixing of 20%~40% crustal material during the subduction process.