Abstract：The Xiaoxia anticline in the northeastern Qinghai-Tibetan Plateau forming during the Cenozoic is one basement-involved fold. This study shows that the formation of the anticline at least underwent two deformation events. Due to the Indo-Eurasian collision in the Early Cenozoic (~49Ma),, the Xining basin had rotated clockwise. In this deformation, early northwest-southeast trending faults in the basement and new-born faults moved right-laterally, which resulted in the development of the northwest-southeast trending fold of cover layers. During the Middle-Late Cenozoic (49－5Ma), owing to the left-lateral strike-slipping of the north and south boundary faults of the Xining baisn, the early north northeast striking faults and new-born R’ faults were active, which resulted in the development of the present north-northeast trending Xiaoxia anticline. Structural analysis shows that these north-northeast trending penetrative faults made the basement show some characteristics of ductile deformation macroscopically. The faulting was the main type of deformation in the basement, however, the sedimentary cover was mainly deformed by flexural bending, all these are similar to Trishear deformation. The formation of the Xiaoxia anticline shows that the development of early faults in the basement is one of important factors controlling the basement-cored folds, and the thickening of the lower crust of the plateau may be related to the development of the basement-involved fold.