Aim: The aim of this study is to investigate the effectiveness of a group-based intervention of patients with T2DM on self-efficacy. The main objective of the study was to explore the appropriateness and feasibility of diabetes intervention as a motivational strategy to enhance self-care of patients with T2DM and its possible integration in primary care from health professionals. Materials and Methods: A quasi -experimental study was conducted with a pre- and post-test design in an experimental group and a control group, in Larissa Greece, at the patients with T2DM during their regular visits in Primary Care Units. Results: The study samples were comprised 2 groups from forty one patients each. None of the patients in either group had received intervention programme previously. The study was conducted throughout in 4 sessions during the period of 3 months. Self-efficacy scores in intervention group differed statistically significantly in all items before and after the experimental procedure, (p<0.05). Intervention group achieved significantly higher scores compared with the control group in certain items (Diet, Medical therapy, Medication-feet check, and Physical activity p=0.001, p=0.001, p=0.001 and p=0.007, respectively). Conclusions: Our study confirms the positive effect of a group-based intervention programme of patients with T2DM on self-efficacy. Future research should assess the viability of group-based intervention to be extended to more adults with T2DM in the community.