AIM: To evaluate the prognostic factors for short-term visual and anatomical improvement of intravitreal ranibizumab (IVR) for diabetic macular edema (DME). METHODS: Fifty-one eyes from 35 patients that received three consecutive monthly IVR for DME with moderate visual loss were retrospectively recruited; all cases had their baseline best-corrected visual acuity (BCVA) between 20/400 and 20/40. BCVA and central subfield thickness (CST) at baseline and month 3 were collected. Linear mixed models were used to evaluate the prognostic factors for visual and anatomical improvement at month 3. RESULTS: Younger age, poorer baseline BCVA and proliferative diabetic retinopathy (PDR) were correlated with better visual improvement at month 3 (P=0.002, 0.0001 and 0.007, respectively). Thicker CST and the presence of subretinal fluid at baseline were correlated with a greater reduction in CST (P<0.0001 and P=0.018, respectively). The presence of epiretinal membrane or previous posterior subtenon injection of triamcinolone acetonide (PSTA) were associated with a smaller reduction in CST (P=0.029 and 0.018, respectively), but had no significant effects in visual improvement at month 3 (P>0.05 for both). CONCLUSION: For eyes with DME and moderate visual loss, those with younger age, poorer baseline BCVA or PDR tend to have better visual improvement after three consecutive monthly IVR. Epiretinal membrane or previous PSTA result in less resolution of CST, but do not significantly affect visual improvement.