The free vibration of the functionally graded isosceles triangular microplates in thermal environments is investigated. The modified strain gradient theory together with the first-order shear deformation theory of plates is adopted to formulate the problem. The material properties are assumed to be graded in the thickness direction. The Chebyshev–Ritz method is chosen as the solution procedure. After demonstrating the fast rate of convergence and accuracy of the method, the effects of temperature rise, length scale parameters, material gradient index, different boundary conditions, apex angle, and width-to-thickness ratio on the free vibration of triangular microplates are studied.