Observation of lower limb kinematics is essential for the characterization of gait and related activities disorders. Robust, flexible and easy to use measurement systems are precious for patients’ follow-up in different medical domains. This study aims to characterize a lower limb optical tracking system based on one detector and seven active markers. Post-processing, which includes skeleton reconstruction and joints’ angular position calculation, is integrated as part of the data acquisition approach. Evaluation of the repeatability of measurements is done through intrasubject gait analysis under repeated runs in identical conditions. The system RMS error is assessed by looking at the dispersion of the calculated distances between the estimated articulations and the markers attached to the body segments. Positional and angular precisions obtained are smaller than 6mm and 2° respectively. Experimental data acquisition is recorded at the average rate of 80Hz. This tool perfectly fits specifications for medical applications. Moreover it presents diverse practical advantages such as its ease of use and its compactness.