<p>The thermoelastic vibration of power-law bidirectional functionally graded material (BFGM) nanobeams considering the influence of different micromechanical models is studied for the first time. The material properties of the nanobeams are temperature-dependent, and they are predicted by four micromechanical models, namely the Voigt, Mori–Tanaka, Hashin–Shtrikman, and Reuss models. Based on the third-order shear deformation theory and Eringen’s nonlocal elastic theory, the governing equations are derived using the transverse shear rotation rather than cross-sectional rotation as an independent variable. Natural frequencies are predicted for BFGM nanobeams with various boundary conditions by the Galerkin finite element method. The result reveals that the micromechanical model is of great importance in predicting the frequencies, and the frequencies obtained by the Mori–Tanaka and Hashin–Shtrikman models are close to each other, while those predicted by the Voigt and Reuss models are the most and the least conservative, respectively. It is also shown that the influence of the temperature rise on the frequencies is more significant for the higher nonlocal parameter. The effects of the material distribution, nonlocal parameter, temperature rise, and aspect ratio on the vibration of the BFGM nanobeams are studied in detail and highlighted.</p>