Abstract: The Koktokay area is located in the southern part of Altay, where Devonian granitoids were well developed and the ages of the granitiods are about 400 Ma. The SiO₂ content ranges from 62.36% to 77.41%, and σ from 0.43 to 1.88, A/CNK from 0.97 to 1.12, implying the granitoid belongs to mid-K, calc-alkaline, quasi-aluminous and weak peraluminous rocks. In addition, they are enriched in LILE(Rb, Th, U) and LREE, obvious depleted of HREE and HFSE(Nb, Ta, Ti), besides, they have island-arc magmatite features characterized by weak-medium negative Eu anomaly. Combined with the regional geological data, the Devonian granitoids is a product of Paleo-Asian Ocean subduction toward north, and generated in an island-arc setting of active continental margin.