Abstract： Objective To observe the efficiency and safety of a single intravitreal injection of Bevacizumab(Avastin)in patients with diabetic macular edema. Methods Prospective,open-label study of 18 eyes of 18 patients with diabetic macular edema which was diagnosed by examination of regular inspection,fundus fluorescein angiography(FFA)and optic coherence tomography(OCT).The patients without general or partial surgery contraindications,aged from 34-75 years with a mean age of 54±11years.The best corrected visual acuity of logMAR was 1.023±0.45 and the retinal thickness of macular foveal was 486 pm before the treatment.The eyes have intravitrealjnjection with Bevacizumab at dose 1.5mg(0.06 ml).After the treatment,the follow-up period ranging from 12 to 20 weeks(mean 16±4weeks).The changes of visual acuity.intraocular pressure.OCT and FFA before and after the treatment were observed and analyzed. Results All 18 patients had a mean IogMAR BCVA of 1.023±0.45 at baseline and at the follow-up weeks 1,4,12,the mean IogMAR BCVA was significantly improved as 0.864±0.48(P=0.001),0.739±0.51(P=0.003),0.792±0.50(P=0.015)respectively,and thedifferences are statistically significant compared with before.Sixteen eyes(88.9%)had a improved orstable visual acuity,the BCVA increased 2 lines(0.2 logMAR vision)or better in 10 eyes(55.6%)anddecreased in 2 eyes at 1 2 weeks after injection.OCT demonstrated that retinal thickness of macular foveal decreased from 486 pm to 413 μm at 4 weeks,decreased to 383μm at 12 weeks(P=0.002,P=0.001),and the differences are statistically significant compared with before.There are remarkable resolution of central retinal edema in 13 eyes(72.2 %)at 12 weeks after the injection.No local or systemic adverse events were observed in any patients. Conclusions The preliminary result in our observation showed that intravitreal injection of Bevacizumab therapy was well tolerated with a significant improvement in BCVA and decrease in macular edema for patients with diabetic macular edema. A randomly controlled muhicenter clinical trial is necessary.