The objective of this work is to investigate the size-dependent nonlinear behavior of mi-crobeams carrying concentrated mass based on strain gradient elasticity theory. Hamilton’s principle is utilized in conjunction with the basic equations of strain gradient elasticity to ob-tain the governing equations of motion and associated boundary conditions. The correspond-ing eigen-value problem is analytically solved to obtain size-dependent natural frequencies of the system. Furthermore, the effect of different higher-order boundary conditions on the mo-tion of the microbeam is investigated .The linear mode shapes of the system are employed along with the Galerkin method to derive the nonlinear temporal equations govern the large amplitude vibration of the microbeam. These nonlinear coupled equations are analytically solved using a perturbation analysis. The numerical simulation of the system is carried out and the effects of different boundary conditions on the time responses of the system is inves-tigated.

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