Objective  To evaluate the appropriate timing for vitrectomy in penetrating eye injuries involving the posterior segment. Methods  Cases series study. Cases were selected from the database of the Eye Injury Vitrectomy Study （EIVS）， which was a multicenter cohort study established in 1997. Patients were classified into three groups based on the time that had elapsed between injury and vitrectomy： 4-14 days， 15-28 days and ≥29 days. Two main vision outcomes of injured eyes were assessed： favorable outcome （better than 4/200） and unfavorable outcome （no light perception -4/200）. Data were analyzed using Kruskal-Wallis and Spearman. Results  There were 12， 11 and 9 cases in the 4-14 days， 15-28 days and ≥29 days groups， respectively. There were no statistically significant differences in age， BCVA after injury， scleral wound， ciliary body damage， retinal detachment， or choroid damage among the three groups. The probability of the incidence of proliferative vitreoretinopathy （PVR） increased following an increase in the interval between the injury and vitrectomy （r=0.622， P<0.01）. Favorable vision outcomes were 9 cases， 4 cases and 1 case in the three respective groups. The probability of a favorable vision outcome decreased following an increase in the interval between the injury and vitrectomy （r=-0.468， P<0.01）. The Fisher exact test showed that visual outcomes from penetrating eye injuries involving the posterior segment that were treated with vitrectomy 4-14 days after injury were better than vitrectomies performed ≥29 days （P<0.01）. Vision improvement rate was negative correlated with interval between the injury and vitrectomy （r=-0.532， P<0.01）. Conclusion  The probability of PVR increased with a greater lapse in time. Thorough vitrectomy should be performed on patients no later than 14 days after open-globe injury.