Because morbidity and mortality rates of diabetes mellitus have been increasing during recent years in Taiwan, how to prevent and manage this disease has become an important issue today. The purposes of this study were to investigate the factors, which influence glycemic control, and to examine the differences in self-management models between good and poor glycemic control outpatients. A total of 66 subjects (31 subjects in the poor control group; 35 subjects in the good control group) were selected by purposive sampling from a medical center. Data were collected in semi-structured interviews and were analyzed by content analysis and SPSS software. The results of this study demonstrated that both education levels and body weight were significantly related to glycemic control. Significant differences in self-management models of diet-control and taking oral medications were observed between two groups. There were no significant differences in self-management models of insulin injection and exercise between the two groups, however. The findings of this study may help nurses to develop nursing intervention to improve a patient’s self-management in glycemic control.