An Inertial Motion Capture System (IMCS) with wireless communication was developed to evaluate the knee joint angle during stair climbing. Two tests were performed, the first one had 10 young subjects (age=20-25 years) in healthy conditions and the second test had only one hemiplegic older adult subject (age=75 years). As a first phase, the knee joint angle was measured from the 10 young subjects using the IMCS developed in order to visualize the movement patterns and analyze the maximum, minimum and average values obtained. In the second phase, the IMCS developed was tested in parallel with the AKTOS IMCS (commercial equipment) to monitor a different activity (walking) and validate the data obtained. The third phase are the results; the knee joint angle was measured in the hemiplegic older adult subject using both IMCS devices to obtain the typical movement pattern. The data was provided by the graphical user interface of the IMCS denoting an average right and left knee angular amplitude of 73.44° and 75.77° respectively, compared to the 10 healthy subjects who presented an average amplitude of 109.73°±8.03° (right knee) and 108.74°±12.18° (left knee). In addition, a different movement curve is denoted and the typical pattern of this hemiplegic subject occurs between the "Pull-up"and "Forward continuance"phases of the stair-climbing cycle.