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A low-cost navigation system, consisting of a Garmin N17 GPS and an inertial sensor unit, was developed for autonomous off-road vehicles. The inertial sensor unit consisted of three single-axis MEMS gyros and one triaxial MEMS accelerometer. This navigation system employed a position-velocity-attitude (PVA) based fusion algorithm to integrate the data sensed by the GPS and inertial sensor unit to provide accuracy vehicle navigation information. The system was evaluated at three different test sites. A highly accurate real-time kinematic differential GPS (RTK-DGPS), which has a dynamic positioning accuracy of 2 cm, was used to provide the reference navigation information. Evaluation tests showed that, when the vehicle was traveling on a paved road around buildings and under the trees, the maximum error of the system was 0.50 m. When the vehicle was traveling in an open field area, the maximum error was reduced to 0.30 m. The system had a position update rate of 50 Hz even though the GPS could only provide a 1 Hz update rate. The navigation system could accurately provide navigation information when the GPS lost the signal for up to 30 s. The evaluation tests verified that the low-cost navigation system could provide accurate and prompt navigation information for some off-road vehicle applications.