Apatite fission track(AFT)analysis on samples collected from a Paleozoic series is used to constrain the cooling history of the Bogda Mountain,northwest China.AFT ages range from 136.2 to 85.6 Ma and are younger than rock depositional ages and the mean confined track lengths(11.0e13.2 mm)mostly showing unimodal distribution are shorten,indicating significant track-annealing.Thermal histories modeling based on the distribution of fission-track lengths combined with the regional geological data show that two rapid cooling phases occurred in the latest Jurassiceearly Cretaceous and the OligoceneeMiocene.Those new data together with previous published data show that the AFT ages become younger from the southwest to northeast in the western Bogda Mountain and its adjacent areas.The fission-track ages of the southwest area are relatively older(>100 Ma),recording the earlier rapid uplift phase during the late JurassiceCretaceous,while the ages in the north piedmont of the Bogda Mountain(namely the northeast part)are younger(<60 Ma),mainly reflecting the later rapid uplift phase in the OligoceneeMiocene.The trend of younger AFT ages towards the northeast might be explained by post-Cretaceous large-scale crustal tilting towards the southwest.In the thrust fault-dominated northern limbs of the Bogda Mountain,AFT ages reveal a discontinuous pattern with age-jumps across the major fault zones,showing a possible strata tilting across each thrust faults due to the thrust ramps during the Cenozoic.The two rapid uplift stages might be related to the accretion and collision in the southern margin of the Asian continent during the late Jurassic and late Cenozoic,respectively. Apatite fission track (AFT) analysis on samples collected from a Paleozoic series is used to constrain the cooling history of the Bogda Mountain, northwest China. Avance range from 136.2 to 85.6 Ma and are younger than rock depositional ages and the mean confined track lengths (11.0e13.2 mm) mostly showing unimodal distribution are shorten, indicating significant track-annealing.Thermal histories modeling based on the distribution of fission-track lengths combined with the regional geological data show that two rapid cooling occurred in the latest Jurassiceearly Cretaceous and the Oligocenee Miocene.Those new data together with previous published data show that the AFT ages became younger from the southwest to northeast in the western Bogda Mountain and its adjacent areas. The fission-track ages of the southwest area are relatively older (> 100 Ma ), recording the earlier rapid uplift phase during the late Jurassice Ceretaceous, while the ages in the north piedmont of the Bogda Mountain (namel the northeast part) are younger (<60 Ma), mainly reflecting the later rapid uplift phase in the Oligocenee Miocene. The trend of younger AFT ages towards the northeast might be explained by post-Cretaceous large-scale crustal tilting towards the southwest. the thrust fault-dominated northern limbs of the Bogda Mountain, AFT ages reveal a discontinuous pattern with age-jumps across the major fault zones, showing a possible strata tilting across each thrust faults due to the thrust ramps during the Cenozoic.The two rapid uplift stages might be related to the accretion and collision in the southern margin of the Asian continent during the late Jurassic and late Cenozoic, respectively.