Purpose: to assess the effectiveness of the therapeutic effect of melatonin on carbohydrate, fat metabolism, and psycho-pathological indicators of patients with type 2 diabetes mellitus (DM). Object and research methods. Our study included 60 patients with type 2 DM and melatonin deficiency: 31 women and 29 men (the average age 48.0±4.2 years). Patients were divided into 2 groups of 30 people: the main group, which received melatonin treatment, and the control group, which received traditional type 2 DM therapy. Patients in the main group took melatonin at a dose of 3 mg 1 hour before bedtime for 2 months while receiving traditional oral therapy for type 2 DM. Monitoring of melatonin in saliva, metabolic and psychological indicators was carried out before the beginning and at the end of the treatment course. The degree of severity of psychological indicators was measured using the DASS21 questionnaire. Results. In the main group after 2 months of treatment, normalization of melatonin levels was observed, significant improvement of the following indicators: HbA1C, HOMA index, reduction of total cholesterol levels and psycho-pathological symptoms (p<0.05). In the control group after 2 months, no significant increase in melatonin levels was observed, as well as improvement of HbA1C, HOMA index. A decrease in total cholesterol levels was noted. Psycho-pathological symptoms either worsened (depression) or did not change significantly (anxiety and stress). Conclusion. A significant positive effect of melatonin at a dose of 3 mg for 2 months was observed on the metabolic parameters of patients with type 2 DM and the improvement of their psycho-emotional state.