Abstract: The Da Hinggan Mountains in Northeast China are typically characterized by extensive and large-scale Mesozoic magmatism.The temporal-spatial distribution and petrogenetic type of the magmatic rocks offer a potential method for constraining tectonic background and geodynamic mechanism.This paper reports the LA-ICP-MS zircon U-Pb ages and geochemical data for the Late Mesozoic granitic rocks in Jifeng area of the Da Hinggan Mountains.U-Pb age data show that magmatism in Jifeng area can be subdivided into two stages:ca.145.2 Ma and ca.124.2~125.8 Ma.The magmatic rocks in two different stages show consistent geochemical characteristics of high SiO₂ (66.88%~75.03%), high Al₂O₃ (13.26%~16.44%), high Na₂O+K₂O (7.35%~9.30%) and high zircon saturation temperature as well as enrichment of LILE and depletion of HFSE.What's more, most of samples display characteristics of Ga/Al×10000>2.6 and Zr> 250×10^-6.These rocks were considered to be the highly-fractionated A-type granite, indicating a regional crustal extension background.In combination with a large number of precise geochronological data between 170~100 Ma published for the Da Hinggan Mountains and their vicinities in the last few years, the authors hold that the first stage A-type granites may be products of partial melting of the lower crust under the tectonic background of transformation from compression to extension controlled by Mongol-Okhotsk Tectonic Domain, while the second stage A-type granitic rocks might have resulted from delamination of thickened lower crust under the tectonic setting of strong stretching.