Abstract: One chemical separation method used in mineral composition separation of the di-nosaur skeletal fossils is introduced in detail in this paper,and the chemical separation and instrumental neutron activation analysis(INAA)of the dinosaur skeletal fossils from Kai-jiang,Sichuan have been made.The biogeochemical study of the analytical results shows that the highly anomalous Ba,U and rare earth elements may well result from burial diage-nesis of the dead dinosaurs;it should not be responsible for mass extinction of dinosaurs. The high anomalies of As,Cr and Rb elements and low anomalies of Zn element in the fos-sils should be caused by the food chains and surrounding media,and thus may lead to the mass mortality of the dinosaur faunas in the study area.