The purpose of this study was to identify factors potentially associated with asthma self-care behavior among adult asthma patients. A correlational descriptive study was conducted with a convenience sample of 220 adults identified as having moderate-to-severe asthma and receiving outpatient care at a medical center in northern Taiwan. Participants were interviewed by questionnaires. The study found that asthma self-care behaviors were predicted by 5 factors: (1) younger age, (2) not smoking history, (3) better social support, (4) better knowledge, and (5) better skills regarding asthma self-care, accounting for 51.5% of the total variance. The study also showed that the initial model could be modified to obtain a recursive model with good fit. Determinant factors identified by the analysis highlight the need to educate adult asthma patients about self-care to minimize mortality and promote their quality of life.