<p>This research investigates the nonlinear thermal buckling behavior of spherical shells composed of functionally graded carbon nanotube-reinforced composites (FG-CNTRCs). The study models the through-thickness CNT distribution as either uniform or functionally graded. The governing equations are formulated using first-order shear deformation theory (FSDT), incorporating Sanders' kinematics and von Kármán-type geometric nonlinearity. Temperature-dependent material properties further introduce material nonlinearity. Thermally induced prebuckling stresses are obtained via linear bending analysis. Stability equations are derived based on the adjacent equilibrium criterion to detect bifurcation points and are discretized using the generalized differential quadrature (GDQ) method in the meridional direction, with Fourier expansion in the circumferential direction. The resulting nonlinear eigenvalue problem is solved iteratively to determine the critical buckling temperature and corresponding mode shape. Parametric studies reveal the significant influence of geometric and material nonlinearities, as well as CNT distribution patterns and boundary conditions, on the thermal stability of FG-CNTRC spherical shells.</p>