This paper presents size dependent formulations based on nonlocal elasticity theory and third order shear deformation theory. The formulations are then applied to the bending analysis of functionally graded rectangular nanoplates with simply supported boundary condition. Similar to functionally graded macro plates, it is assumed that the material properties of nanoplates are varied across the thickness direction by a power rule of the volume fraction of the constituents. Numerical results illustrate the influence of the power-law exponent and the nonlocality on the deflections of simply supported rectangular nanoplates.