People with diabetes have a much higher risk of impaired cognitive function due to increased vascular aging. Brain-derived neurotrophic factor (BDNF) is one of the most important neurotrophins due to its characteristics, such as protecting neuronal tissue and improving the function of the central nervous system. BDNF level might be related to different factors are age, glucose, drug in Tip II diabetes (T2DM) patients. We have aimed to investigate the association between serum concentrations of BDNF and blood parameters in diabetic patients. Forty-six T2DM patients have been enrolled in this observational study. Serum BDNF, cognitive, hematologic, and biochemical parameters were measured in metformin-taking patients (n=29, Group I) and patients without metformin therapy (n=17, Group II). BDNF, age, gender, blood, and cognitive parameters were statistically insignificant between the groups. BDNF serum level was positively correlated with glucose in all patients (p=0.013). Metformin is the most commonly used anti-diabetic in the treatment of T2DM. Despite many studies indicating the pro-cognitive effects of both metformin and BDNF, our results indicated that there were no significant differences between a specific groups of DM patients suggesting that further studies, including also specific age and disease groups, are needed to clarify the specific role of BDNF and metformin in cognition.