Objective To observe the survival of human umbilical cord derived mesenchymal stem cells (hUC-MSCs) after injection into the vitreous of rabbits,and the animal safety under those procedures.Methods Twenty-seven pigmented rabbits were randomly divided into 3 groups (intravitreal injection 1 week group,2 weeks group and 4 weeks group),each with 9 rabbits.For each animal the right eye was the experimental eye receiving hUC-MSCs injection,while the left eye was the control eye receiving cuhure medium.The rabbit eyes were examined by slit-lamp microscope,indirect ophthalmoscopy,fundus photography,fundus fluorescence angiography(FFA)and Tono-pen tonometer before and after injection.hUC-MSCs were labeled by CM-Dil in vitro,and their survival status was measured by eonfocal fluorescence microscopy,light microscope and transmission electron microscope at 4 weeks after injection.Results Four weeks after injection,a large number of the hUC-MSCs were still alive in the vitreous cavity.The overall condition of those rabbits was good.The anterior segment and retina of experimental eyes were normal,without hyperfluorescence,hypofluorescenee and leakage in the retina at 1,2 and 4 weeks after injection.There was no significant difference on lOP before and after injection at different time points (P>0.05),and no obvious changes at cornea,anterior chamber angle,lens,retinal structure by.light microscope and transmission electron microscope examination.Conclusion hUC-MSCs can survive in the rabbit vitreous for four weeks;intravitreal injection of hUC-MSCs was safe and feasible.