In this paper we numerically investigate the chaotic behaviours of the fractional-order Lorenz system and its synchronization. For the first time, a fractional chaotic synchronization using an Unscented Kalman Filter (UKF) is presented. The chaotic synchronization is implemented by the UKF design in the presence of process noise and measurement noise. To illustrate the effectiveness of the synchronization with the UKF method, a numerical example based on the fractional-order Lorenz dynamical system is presented and the results are compared to the Extended Kalman Filter (EKF) method.