Background: Diffuse diabetic macular edema (dDME) is one of the most frequent squeal of diabetes mellitus and deteriorates visual acuity in the working group of population. Purpose: to compare the effectiveness of intravitreal ranibizumab alone or ranibizumab combined with thermal laser therapy for treatment of diffuse diabetic macular edema. Patients and methods:forty five eyes of 45 patients suffering from diffuse diabetic macular edema were requriuted and classified into two groups; intravitreal ranibizumab alone group (IR group) included 24eyes of 24 diabetic persons, injected with 0.5 mg ranibizumab (0.1ml) at baseline, 1st month, and 3rd month. A twenty-one eye of 21 diabetic patients was injected with 0.5 mg ranibizumab at baseline, 1st month, and 3rd month followed with macular grid argon laser photocoagulation three weeks after the 1st injection (combined group). Visual acuity as log MAR value, central macular thickness (CMT) measured with optical coherence tomography (OCT), and intraocular pressure (IOP) were assessed at baseline, 3 and 6 months post-injection. Results: the baseline log MAR visual acuity and macular thickness significantly improved in both groups at three, and six months post-injection. However, the combined group showed more improvement with stable results at the end of follow up period of six months. The mean IOP was 14.1±1.3 mmHg and 13.9±1.4mmHg at the end of follow up in IR and combined groups respectively. Conclusion: both groups achieved improvement of visual acuity and reduction of the macular thickness but the effect was more pronounced and long-lasting in the combined therapy group.