<p>This paper investigates the nonlinear free vibration of sandwich plates with carbon nanotube (CNT) reinforced composite core subjected to uniaxial compressive loads in thermal environments. Unlike previous studies, CNTs are reinforced in core layer to optimize the performance of sandwich plate. The CNTs are reinforced into matrix phase through functionally graded distributions. The properties of constitutive materials are assumed to be temperature-dependent and effective properties of nanocomposite are determined using an extended rule of mixture. Motion and compatibility equations are derived within the framework of first-order shear deformation theory taking into account von Kármán nonlinearity and geometric imperfection. All boundary edges are simply supported, and two uncompressed edges are elastically restrained against tangential displacement. Analytical solutions and Galerkin method are employed to solve governing equations and obtain a nonlinear ordinary differential equation. Fourth-order Runge–Kutta numerical integration scheme is applied to compute the nonlinear frequencies of sandwich plates. The results indicate that the uniaxial compressive loads decrease and strengthen the natural frequencies and frequency nonlinearity of sandwich plates, respectively. The study also reveals that the frequency nonlinearity is more significant when the unloaded edges are restrained more rigorously and temperature is more elevated. Furthermore, the analysis detects that the natural frequencies and frequency ratios respectively are the highest and lowest for a relatively small value of thickness of face sheets.</p>