In this paper we present a practical algorithm of land-vehicle integrated INS/GPS system based on Monte-Carlo type nonlinear filtering and show experimental results of using the actual GPS and INS data. Closed-loop chanization is adopted for our navigation system by integrating Inertial Navigation System (INS) and the code-based transfer Differential GPS (DGPS) which gives the position (latitude, longitude) and the Doppler velocity. Our aim is to integrate the advantages of these systems and to develop the navigation system that does not require initial attitudes information of the vehicle.