Purpose. Tripping over objects is a major cause of fall-related injuries. The elderly feature decreased locomotor velocity with aging and delays in locomotion when encountering obstacles. Numerous studies have analyzed how the mobility performance of the elderly is affected when crossing over an obstacle. However, how is mobility performance affected when performing sequences of various locomotor movements (gait, changing direction, standing up and sitting down) that make up activities of daily living? To answer this question, this study investigated the changes in locomotor velocity when encountering an obstacle during various locomotor movements in both older adults and young adults by using the TUG, a representative mobility test. Methods. Thirty older adults who were judged to be able to walk independently by the Berg Balance Scale (BSS) (age: 70.0 ± 6.94 yrs; BB S: 54.7 ± 1.78 pts) and seventeen male young adults (age: 21.7 ± 2.37 yrs) participated in the “Timed Up & Go” (TUG) test with and without an obstacle. Using the TUG score (the total time required to complete the test), a rate of the total times (with an obstacle/ without an obstacle) was calculated to create an index of the decline in mobility performance by the obstacle. Results. The decline in the mobility performance of the elderly was significantly larger than the young adults for the following measurements: in the single stance phases just before and after an obstacle, the time needed to change direction 180 degrees, and for level walking after crossing over an obstacle. Conclusions. The elderly require a longer period of time for stepping over obstacles. Gait and the ability to change direction after encountering an obstacle was found to be slower when compared to the younger male population.