<p>Porous materials with high energy absorbance capacity are widely incorporated into sandwich construction to reduce the vibration of structures. This paper presents a size-dependent beam model for studying thermoelastic nonlinear dynamics of sandwich microbeams with an functionally graded porous (FGP) core under a moving mass. Considering both the shear deformation and rotary inertia, the beam model based on the sinusoidal beam theory is derived by using the modified couple stress theory (MCST) to capture the microstructural size effect. The nonlinear differential equations of motion with temperature-dependent material properties are established and then transferred to a discretized form using an finite element formulation. The nonlinear dynamic response of the sandwich microbeam with simply supported ends is predicted using the Newton–Raphson iterative procedure in conjunction with the Newmark method. The result reveals that while the effect of porosities on the nonlinear dynamic response is more significant for the sandwich beam having a larger core thickness, that of temperature change decreases as increasing the porosity coefficient. The influence of the porosity distribution, temperature change, the Coriolis and centrifugal forces induced by the moving mass on the nonlinear dynamic behavior of the sandwich microbeams is studied in detail and highlighted.</p>