For mobile mapping system, the integration of inertial navigation system (INS) and global positioning system (GPS) is widely applied as the main component of the direct geo-referencing system to determine position and orientation. For real-time applications, Kalman filter is often used as the main estimator for data fusion and backward smoothing is considered an optimal post-processing procedure. This study apply smoothing algorithm in a real-time INS/GPS integrated system to on-line update smoothed states at near real-time rate. To verify the effectiveness of the proposed method, field tests with different testing scenarios are implemented in comparison with reliable reference data.