A parameter observer is designed to identify Rossler system with unknow parameters. Chaos synchronization between uncertain Rossler system and Coullet system is realized via backstepping method.The synchronization controller is presented based on stability theory, and the area of controlling gain is determined. The simulation results show that all the state variables in the Coullet system can track any desired trajectory in the Rossler system exactly when the parameter observer and backstepping controller are functioning, which shows the method is effective and feasible.