Background Diabetic macular edema (DME) is a common manifestation of diabetic retinopathy (DR) that forms the main cause of central visual impairment. This study aimed to compare the efficacy and safety of a single intravitreal injection of bevacizumab alone versus bevacizumab combined with triamcinolone acetonide in eyes with diabetic macular edema (DME).Methods A total of 40 eyes in 40 Chinese patients (22 male and 18 female) diagnosed with diabetic macular edema were enrolled in this prospective, randomized, consecutive study. Among them, 21 patients in group 1 were treated with intravitreal injection of bevacizumab (1.25 mg/0.05 ml), and the other 19 patients in group 2 accepted intravitreal bavacizumab (1.25 mg/0.05 ml) combined with triamcinolone acetonide (2 mg/0.05 ml). All patients were examined at baseline and followed up at 4, 6 and 12 weeks after the injection. Changes in mean best correct visual acuity (BCVA)using ETDRS chart, central retina thickness (CRT) measured by optical coherence tomography (OCT), and intraocular pressure (IOP) were focused on.Results In group 1, mean BCVA improved from (41.76±15.59) letters (baseline) to (56.24±18.56)letters, (52.5712.31)letters and (48.41±17.90) letters at 4, 6 and 12 weeks post-injection, respectively (P=0.004, P=0.011 and P=0.026,respectively). Mean CRT decreased from (525.76±184.10)μm(baseline) to (270.33±202.67) μm, (303.12±168.43) μm and(402.26±196.21)μm, respectively (P=0.009, P=0.016 and P=0.030, respectively). In group 2, mean BCVA improved from (39.89±12.27) letters (baseline) to (55.31±19.27) letters, (51.25±13.48) letters and (46.97±16.23) letters at 4, 6 and 12 weeks after injection, respectively (P=0.003, P=0.010 and P=0.027, respectively). Mean CRT decreased from (554.50±169.05)μm(baseline) to (292.76±196.05)μm, (323.46±164.05) μm and (426.38±169.05) μm, respectively (P=0.009, P=0.014 and P=0.028, respectively). However, there was no significant difference between these two groups with regard to mean BCVA (F=1.602, P=0.216) and CRT (F=0.412, P=0.526). At 12 weeks after the injection, 11 of the patients in group 1 and nine patients in group 2 appeared recurrent macular edema and needed repeat injections. There was one patient in group 2 appeared transient intraocular pressure increases.Conclusions Intravitreal injection of bevacizumab combined with/without triamcinolone acetonide had a beneficial effect on DME. However, the significant effect was not permanent. Our results showed that no significant differences were detected between intravitreal bevacizumab combined with/without triamcinolone acetonide for the eyes with diabetic macular edema in Chinese patients.