Introduction: The aim of this study was to investigate the moderating role of coping strategies in the relationship between illness perception, quality of life and HbA1c in patients with type I diabetes. Materials and Methods: Three hundred patients (172 females and 128 males, 18-30 years) aged with type I diabetes from the Iranian Diabetes Society completed the Illness Perception Questionnaire (IPQ), Coping Inventory for Stressful Situations (CISS), and Quality of Life scale for Diabetics (D-39). HbA1c level was obtained from patient`s laboratory examination. Results: Results of stepwise regression analysis revealed that the influence of illness perception on HbA1c was moderated by task-oriented coping strategy. The relationship between illness perception and quality of life was influenced by three coping strategies, task oriented, emotion-oriented, and avoidant. Conclusion: Coping strategies affect the relationship between illness perception, quality of life and HbA1c in patients with type I diabetes. Results can be helpful in devising preventive policies, determining high risk patients and designing of psychological interventions.