BackgroundGlycaemic control is the main goal of treatment for type 2 diabetic patients. Hyperglycaemia may result in cognitive decline. More family support may increase medication adherence and decrease glycaemic level. The purpose of this study was to determine the impact of family support improvement behavior on anti diabetic medication adherence and cognition in type 2 diabetic patients.MethodThe randomized control trial study was conducted on 91 patients from an outpatient diabetes clinic. They were randomly divided to intervention (n = 45) and control (n = 46) group. Data on the patients’ demographic information and their family gathered using a questionnaire, For two groups Morisky Medication Adherence Scale (MMAS), drug administration part of Diabetes Social Support Questionnaire – family version (DSSQ), Number Connection Test (NCT) were applied and hemoglobin A1C was measured two times in the onset of study and three months later for control group and before and after intervention for intervention group. The key family members of the intervention group were taught according to their educational needs in small groups.ResultIn intervention group mean of NCT score was significantly decreased after intervention (P = 0.006) however in the control group there was no significant difference after three months. In intervention group a significant correlation was noted between DSSQ scores and MMAS scores after intervention(r =0.67, P < 0.001) but, there was no significant correlation in the control group.ConclusionFamily support instruction based on the educational needs of family members, may improve medication adherence through direct effect and cognitive status with indirect effect.