Abstarct: This paper presents thermal post-buckling behavior of functionally graded carbon nanotube-reinforced composite (FG-CNTRC) beams in thermal environments and under various boundary conditions. The material properties are simulated to be graded in the thickness direction, and temperature dependency of the constituents is also considered. It is assumed that the beam is subjected to both uniform and non-uniform temperature rises. To take into account the transverse shear strains, various shear deformation theories namely, the first-order and higher-order shear deformation theories utilized for theoretical formulations. The governing equations are derived baxsed on von Kármán geometric nonlinearity with equilibrium equations and including thermal effects. The differential quadrature method with an iterative algorithm as a nonlinear solution scheme is adopted to solve the governing partial differential equations, determine the critical buckling temperatures and the thermal post-buckling equilibrium path of FG-CNTRC beams. By comparing the results with those of existing in the literature, the applicability, convergence, and accuracy of the DQ method are verified. The influences of each considered shear deformation theories, distribution pattern and volume fraction of carbon nanotubes, boundary conditions and slenderness ratio on the thermal buckling and post-buckling performance are discussed in details. The results indicate an FG-CNTRC beam under a uniform temperature rise is more likely to buckle compared with the non-uniform temperature variation. Our numerical results showed that a CNTRC beam with an intermediate CNT volume fraction does not necessarily have intermediate buckling temperature and post-buckling equilibrium path. Also, the FGX-CNTRC beam has the highest buckling temperature and thermal post-buckling equilibrium path, followed by UD- and FGO-CNTRC beams. baxsed on the post-buckling response, it is also found out that the effect of shear deformation may be neglected if the slenderness ratio reached to a specific amount for UD-CNTRC and FGX-CNTRC beams.