In order to determine whether cognitive demand disrupts balance and walking patterns for the elderly, a total of twelve healthy seniors and fifteen healthy young adults are recruited to complete three tasks: a single primary task (obstacle crossing), a single secondary task (pressing a button), and dual tasks (obstacle crossing and pressing a button). Two in-series force platforms and a three-dimensional six-camera motion analysis system are used to record the ground reaction forces and motion data, respectively. A stimulus tone is produced and the reaction time is recorded by STIM2 software. Our results show that aging might increase the stride time and reaction time, while decreasing the walking velocity, the peak center of mass velocity in the anterior/posterior and medial/lateral directions, the medial center of mass and center of pressure inclination angle, and accuracy in the tone discrimination task. In addition, elderly subjects demonstrated a significant increase in stride time, reaction time, and decrease in accuracy of tone detection under the dual-task condition compared to those demonstrated under single-task conditions. Data suggests that elderly subjects adopted a conservative gait strategy to maintain stability and that they were more likely to be distracted under dual-task conditions. Their performance in a cognitive task is thus influenced by locomotion.