Abstarct: Transient nonlinear vibration of micro beam with thermoelastic damping is the main purpose of this thesis. After presenting a brief history of major related researches, the heat conduction equation for nonlinear strain-displacement relation has been solved and the equation of motion for Euler-Bernoulli beam for large lateral displacement with thermoelastic damping is obtained. Moreover amplitude dependent nonlinear modal functions have been obtained via nonlinear normal modes (NNM) theory which was then used to derive the equivalent SDOF system for single mode vibration. The result of transient nonlinear vibration was obtained by harmonic balance method and analytic signal approach. Amplitude dependent thermoelastic damping and its effect on the response parameters was also studied. Finally it's been shown that the obtained equivalent SDOF system in single mode vibration by NNM theory differs significantly from other conventional methods such as Galerkin procedure, which results in extrema points in response parameters during transient vibration.