Purpose: To investigate the effectiveness of two regimens of ranibizumab-assisted pars plana vitrectomy in the treatment of patients with proliferative diabetic retinopathy. Methods: This is a prospective, 6-month, randomized controlled trial. Eighty patients with 87 eyes requiring pars plana vitrectomy treatment for proliferative diabetic retinopathy were included and randomly divided into a 1.0-mg injection group and a 0.5-mg injection group. The ranibizumab was delivered intraoperatively, at the close of surgery. The vitreous hemorrhage grade, best-corrected visual acuity, central macular thickness, and safety data were assessed to Month 6. Results: The 1.0-mg injection group had a milder grade and a lower reoccurrence rate of early postoperatively vitreous hemorrhage than the 0.5-mg injection group (35.0% and 63.4%, respectively, P = 0.0195). The mean best-corrected visual acuity of two groups was significantly improved from baseline to 6 months after surgery, 1.60 +/- 0.72 Logarithm of the Minimum Angle of Resolution (LogMAR) (<20/200) to 0.47 +/- 0.49 LogMAR (20/59) for the 1.0-mg injection group and 1.51 +/- 0.69 LogMAR (<20/200) to 0.50 +/- 0.31 LogMAR (20/63) for the 0.5-mg injection group, but there was no significant difference between the two groups (P = 0.74). There was no significant difference in the mean decrease in central macular thickness and probability of postoperative adverse events between the two groups. Conclusion: Intravitreal injection of 1.0 mg of ranibizumab after pars plana vitrectomy compared with the recommended dose of 0.5 mg significantly reduced the recurrence and severity of early postoperative vitreous hemorrhage in patients with proliferative diabetic retinopathy. It also contributed to the early recovery of visual acuity after surgery and did not increase postoperative adverse events.