Abstarct: Chaos systems have complex dynamics, which are highly sensitive to their initial conditions. In this thesis, synchronization of such systems with several slave systems and system uncertainties is studied. To deal with this problem, an observer-baxsed finite-time control for modified projective mode is discussed. First, a super-twisting observer is introduced to estimate the uncertain terms. Then, a finite-time controller is designed to ensure the synchronization. Afterward, the control parameters is determined by an optimization algorithm in order to minimize the system error. Finally, simulation results are provided to show the effectiveness of the proposed control method in secure communication types, such as masking, inclusion, and cascade inclusion. Due to the ability to synchronize chaotic systems where the master system directs the slave systems using its own output signal, chaotic systems can be used to implement security in communication systems.