Objective: Driving is a complex activity involving cognitive and motor skills. It is an essential component of daily life for older adults. However, aging may decrease a driver’s psychomotor performance and increase the risk of traffic accidents. Driving reaction time (DRT) requires visuo-motor coordination and fast DRTS are needed to cope with unexpected conditions or traffic lights. The purpose of the current study was to compare the DRT of elderly drivers and young drivers using a tri-axial accelerometer and a foot switch. Methods: Twenty-four subjects (younger=12, elderly=12) participated in this study. DRT was measured with a tri-axial accelerometer and foot switch. DRT was classified by initiation and termination as on or off according to contact with the brake pedal during the brake pedal task. Results: The ANOVA model for accelerometer-DRT yielded significant main effects for phase, but not for axis. Termination was delayed significantly more than initiation. The elderly group showed significantly more delay than the younger group. In the elderly group, termination was delayed more than initiation, but there was no difference in delay between initiation and termination in the young group. In foot switch-DRT, termination was delayed much more than initiation in both groups (p<0.05). The elderly group showed significantly more delay than the young group. Conclusion: We suggest that the driving ability of elderly drivers can be assessed with reasonable accuracy using accelerometer-DRT. Application: The result of accelerometer-DRT might help to minimize the expense and risk associated with on-road assessments of this population.