Abstract. This paper presents the integration of Inertia Navigation System and Global Position System (GPS) using Unscented Kalman Filter (UKF). The nonlinear system model is used because linearized system models introduce errors in high dynamic environments. The navigation performance and robustness of the proposed algorithm are also compared with that of the extended Kalman filter (EKF). To enhance the navigation performance, the non-holonomic constraint is applied to the UKF and it is found that the robustness of system is better than before when the GPS signal outages.