Engaging in activities has been found beneficial overall to individuals’ well-being. What has not been systemically tested with large sample data is whether such benefits diminish at very old ages. This study uses the Chinese Longitudinal Health Longevity Survey (CLHLS) between 2002 and 2008 to test how the effect of engaging in activities on mortality changes by age among the elderly. Approximately half of the 16,064 people aged 65 and over interviewed in 2002 died within the following six-years. Two types of activities are examined: customary physical activities, such as such as doing housework and gardening, and social activities, such as playing cards and attending organized activities. The Cox model is applied to analyze the hazards of mortality. Both physical and social activities are found to reduce the hazards of mortality for the whole sample and both activities showed a negative interaction effect with age. As age increases, their beneficial effects decrease. These patterns are also evident in the sub-sample analysis by age and gender. Although many studies have shown the beneficial effect of engaging in activities for individuals’ well-being, as is well reported in the media, these results suggest a diminishing effect at old ages.