This paper addresses passivity-based synchronization method of uncertain modified Colpitts oscillators. Considering the effect of external disturbances on system’s parameters and nonlinear control inputs, a simple-workable robust passivity controller based on Lyapunov theory and linear matrix inequality (LMI) is designed for the output synchronization between a master system and a slave system consisting of uncertain modified Colpitts oscillators. A sufficient criterion is also investigated which can not only ensure the asymptotic stability of the solutions of the error dynamics but also reduce the influence of the disturbance within a prescribed level. The proposed controller can be obtained by solving a convex optimization problem presented by the LMI. In order to verify the effectiveness of the proposed control scheme, some numerical simulations are performed and a Pspice analog circuit implementation of the complete master-slave-controller system is presented.