Objective To observe the efficiency and safety of a single intravi treal 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 54plusmn;11 years. The best corrected visual acuity of logMAR was 1.023plusmn;0.45 and the retinal thickness of macular foveal was 486 mu;m before the treatment. The eyes have intravitreal injection with Bevacizumab at dose 1.5 mg (0. 06 ml). After the treatment, the follow-up period ranging from 12 to 20 weeks (m e an 16plusmn;4 weeks). 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 logMAR BCVA of 1.023plusmn;0.45 at baseline and at the follow-up weeks 1, 4, 12, the mean logMAR BCVA was significantly improved as 0.864plusmn;0.48 （P=0.001）, 0.739plusmn;0.51 (P=0.003), 0.792plusmn;0.50 (P=0.015) respectively, and the differences are statistically significant compared with before. Sixteen eyes (88.9%) had a improved or stable visual acuity, the BCVA increased 2 lines (0.2 logMAR vision) or better in 10 eyes (55.6%) and decreased in 2 eyes at 12 weeks after injection. OCT demonstrated that retinal thickness of macular foveal decreased from 486 mu;m to 413 mu;m at 4 weeks, decreased to 383mu;m 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 observati on showed that int ravitreal 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 multicenter clinical trial is necessary. (Chin J Ocul Fundus Dis,2008,24:172-175)