Purpose: This study was done to investigate the relationship between depression, self-care activity and $HbA_1c$ in clients with type-2 diabetes mellitus (DM) clients. Method: This was a cross sectional descriptive study and data were collected between October 4 and 27, 2006 using a questionnaire. The participants were inpatients and outpatients with type-2 diabetes being seen in one of two hospitals. The questionnaire included general as well as disease related characteristics, a depression scale (CES-D), and the self-care activity scale developed by Kim (1996). $HbA_1c$ was obtained from medical records. Results: There were 50 men (41.7%) and 70 women (58.3%). The mean scores for depression and self-care activity were $18.22{pm}10.03$ and 3.51, respectively. Almost half of the Participants (46.7%) had an $HbA_1c$ greater than 7%. Self-care activity was negatively correlated with depression (r=-.436, p=0.00) and $HbA_1c$ (r=-.269, p=0.03). Depression was positively correlated with $HbA_1c$ (r=-.325, p=0.00). Participants who had diabetes education showed a significantly lower level of $HbA_1c$ than the group who had never had diabetes education. Conclusions: It is Important to make ensure that patients with diabetes have education on diabetes mellitus and to screen and manage depression as part of the care for these patients.