Title Buckling analysis of three-dimensional functionally graded Euler- Bernoulli nanobeams based on the nonlocal strain gradient theory Type Article Keywords Buckling analysis, Strain gradient elasticity theory, Nano beam, Three-directional functionally graded materials (TDFGMs), Generalized differential quadrature method (GDQM). Abstract This paper presents a nonlocal strain gradient theory for capturing size effects in buckling analysis of Euler-Bernoulli nanobeams made of threedimensional functionally graded materials. The material properties vary according to any function. These models can degenerate to the classical models if the material length-scale parameters is assumed to be zero. The Hamilton's principle applied to drive the governing equation and boundary conditions. Generalized differential quadrature method used to solve the governing equation. The effects of some parameters, such as small-scale parameters and constant material parameters are studied Researchers ahmad soieimani (First researcher)Farshad Zamani (Second researcher)Hamid Haghshenas Gorgani (Third researcher)