Although child asthma is an important issue worldwide, child asthma in Taiwan has received little attention. This study attempted to understand the relationship among physical activity, self-efficacy, and quality of life in children with asthma. This study is descriptive and correlational. One hundred and two subjects were recruited from a child allergy clinic in a medical center by purposive sampling. The results of the study indicated that past asthma experience was the most significant factor affecting the self- efficacy of asthmatic children, while vicarious experiences in terms of modeling influence personal beliefs by comparing one's situation with that of another was the least significant factor A significant relationship was found between self-efficacy and physical activity (p ＜ 0.01)、 suggesting that the actual level of physical activity increased along with self-efficacy. However, no significant relationship was found between quality of life and self-efficacy or between quality of life and physical activity. These findings can help health professionals provide more information on type, intensity、and frequency of exercise, and preventative methods related to asthma attach to sick children , parents , and schoolteachers.