The synchronization between two unknown chaotic systems is achieved by designing a controller based on the sliding mode control technique and radial basis function neural network. The controller design method is independent of the system mathematical model, but only depends on the output of the system state. Moreover, it is robust to parameter uncertainties and the outside interference. Finally, synchronization between unknown Lorenz systems and between unknown Lorenz system and Chen system are achieved using the proposed method. The response time is very short and the synchronization performance is good.