To investigate the frequency and factors associated with inadequate self-care behaviors in patients with type 2 diabetes mellitus (T2DM). Methods: A cross-sectional study was conducted on a sample of 355 patients with T2DM, using multistage cluster sampling, attending the Najran University Original Article Hospital and Primary health care centres in Najran, Saudi Arabia, from January to May 2019. The assessment of self-care behaviors was conducted using the 16-item diabetes self-management questionnaire (DSMQ). Results: The majority (85.1%) of the patients with T2DM were uncontrolled, 42% were obese, and 5.9% were morbidly obese. Based on DSMQ criteria, the majority of patients (90.1%) had poor self-care behaviors. The mean sum of DSMQ was 5.04 out of 10. Among the DSMQ subscales, health care use had the highest mean score of 5.63, followed by glucose management with a score of 5.12, while dietary control had lower mean scores of 4.96 and physical activity had 4.46, all were inadequate. Being married (OR=2.178, p=0.035) and having DM for more than 5 years (OR=2.711, p<0.006) were the significant independent factors associated with poor self-care behavior. Conclusion: Inadequate self-care behavior is widely prevalent in Najran city, Saudi Arabia. All the DSMQ subscales were poorly managed by most of the diabetic patients. Furthermore, being married and having a longer DM duration are the significant independent factors associated with poor self-care behaviors.