Slip-induced fall accidents have been recognized as a serious threat to the health of the elderly.The objective of the current study was to investigate the aging effect on the biomechanical reactions of both perturbed foot and unperturbed foot to the unexpected slips. Nineteen younger (mean age: 25.0 years old) and twenty-one older (mean age: 71.2 years old) adults were involved in a laboratory study,in which slippery surface was induced during walking without their awareness.The reactive responses of both slipping foot and unperturbed foot were quantified by optical motion capture system and force platforms.The results indicate a characteristic toe-touch strategy by the unperturbed foot after slip starts. Significant aging effects were found in touch down base of support created by the unperturbed foot. It was concluded that the unperturbed foot is important to facilitate successful recovery from unexpected. Specifically, in order to prevent age-related slip-induced falls, it is important for the unperturbed foot to create sufficient base of support in anterior-posterior direction and to control the base of support in media-lateral direction.