In the present study, thermal buckling analysis of functionally graded carbon nanotube reinforced composite (FG-CNTRC) conical shells is presented. The effective material properties of FG-CNTRCs are determined using the extended rule of mixture. By employing the Hamilton’s principle and based on first-order shear deformation theory and Donnell strain-displacement relations, the governing equations are obtaind. The membrane solution of linear equilibrium equations is considered to obtain the pre-buckling force resultants. Using the generalized differential quadrature method in axial direction and periodic differential operators in circumferential direction, the stability equations are discretized and the critical buckling temperature difference of shell is obtained. The accuracy of the present work are first validated by the results given in the literature and then the impacts of involved parameters such as volume fractions and types of distributions of carbon nanotubes, boundary conditions and geometrical parameters on thermal buckling of functionally graded nanocomposite conical shell are investigated. The results indicate that the values of volume fractions and types of distributions of carbon nanotubes along the thickness direction play an important role on thermal instability of FG-CNTRC conical shells.