Abstract: Due to the variation in material properties through the thickness of functionally graded material (FGM) structures, an FGM beam simply supported at both ends exhibits characteristics quite different from those of a FGM beam clamped at both ends. An exact, closed form solution is obtained for nonlinear static responses of FGM beams subjected to non-uniform in-plane thermal loadings. The equations governing the axial and transverse deformations of FGM beams are derived based on the nonlinear classical beam theory and the physical neutral surface concept. The two equations are reduced to a single nonlinear fourth-order integral-differential equation governing the transverse deformation. For an FGM beam clamped at both ends, the equation and the corresponding boundary conditions lead to a differential eigenvalue problem, whereas for an FGM beam simply supported at both ends, an eigenvalue problem does not arise due to the inhomogeneous boundary conditions. This consequently results in quite different behavior between a clamped and a simply supported FGM beams. The nonlinear equation is directly solved without any use of approximation and a closed-form solution for thermal bending deformation is obtained as a function of the applied thermal load. By using the exact solutions, the nonlinear deformation problems for buckling, postbuckling and nonlinear bending of the beam can be investigated. Finally, the numerical analyses are carried out to investigate the effects of material gradient properties and thermal loads on the nonlinear static responses of FGM beams.