This work studies the size-dependent stability analysis of restrained nanobeam with functionally graded material via nonlocal Euler-Bernoulli beam theory using the Fourier series. The nonlocal elasticity theory introduced by Eringen is utilized to show the size effect on the buckling response of restrained functionally graded nanobeam. In addition, buckling loads of functionally graded nanobeam are obtained by classical elasticity theory as well to highlight the size effects. The influences of various parameters such as the nonlocal parameter, rotational restraints and power-law index on the critical buckling load of the functionally graded nonlocal beam are investigated. The contribution of this paper is that it presents an efficient analytical solution for the buckling response of functionally graded nanobeam with non-rigid boundary conditions.