to suit the functionality of structures. The gradually composition variations of the material constituents from one surface to another provide a proper solution to the problem of induced transverse shear stresses due to the two bonded dissimilar materials with high difference in material properties. Also, due to containing outstanding mechanical properties, FGMs are appropriate for design of engineering structures [1][2][3][4][5][6][7].In recent years, FGMs have been extensively utilized in micro-electromechanical and nano-electromechanical systems and devices [8]. On the other hand, size-dependent structures such as micro and nano scale beams are key components in many systems. Therefore, mechanical analysis of micro/nano beams has received striking attention from research communities. The classical continuum theory which is extensively used in mechanical analysis of macroscopic structures should be extended to consider the size effect on mechanical behaviors of micro/nano structures. Therefore, this can be attained by the nonlocal elasticity theory proposed by Eringen in which a stress state at a reference point is suggested as a function of the strain of all neighbor points. It is noted that some studies are published on mechanical behavior of size-dependent FG beams. Among them, Simsek and Yurtcu [9] investigated bending and buckling behavior of size-dependent FG nanobeam using analytical method and Timoshenko and EulerBernoulli beam models. Also, the static and stability behavior of FG nanobeams based on nonlocal continuum theory studied by Eltaher et al. [10]. Nonlinear free vibration of functionally graded nanobeams within the framework of Euler-Bernoulli beam model including the von Kármán geometric nonlinearity studied by Sharabiani and Yazdi [11]. Also, forced vibration analysis of FG nanobeams based on the nonlocal elasticity theory and using Navier method for various shear deformation theories studied by Abstract This paper investigates buckling response of higher-order shear deformable nanobeams made of functionally graded piezoelectric (FGP) materials embedded in an elastic foundation. Material properties of FGP nanobeam change continuously in thickness direction based on power-law model. To capture small size effects, Eringen's nonlocal elasticity theory is adopted. Employing Hamilton's principle, the nonlocal governing equations of FGP nanobeams embedded in elastic foundation are obtained. To predict buckling behavior of embedded FGP nanobeams, the Navier-type analytical solution is applied to solve the governing equations. Numerical results demonstrate the influences of various parameters such as elastic foundation, external electric voltage, power-law index, nonlocal parameter and slenderness ratio on the buckling loads of sizedependent FGP nanobeams.