Endothelial progenitor cells (EPC) play an important function in vasculogenesis and acquire a capability for vascular repair and formation as they differentiate. We examined the kinetics of EPCs from the viewpoint of EPC biology by creating oxygen-induced retinopathy (OIR) in a mouse model imitating retinopathy of prematurity (ROP), which causes pathological retinal neovascularization. Delayed differentiation, mobilization, and tissue recruitment of EPCs were obvious in the vaso-oblitelative phase, but they were promoted in the vascular proliferative state. Moreover, pathological retinal vasculature in OIR was repaired by the intravitreally transplanted definitive EPCs. These results suggest that delay of bone marrow derived EPC differentiation is a factor of morbid retinal blood vessels' formation in OIR. Aberrant kinetics of bone marrow derived EPC contribute to the formation of the retinal blood vessels, and it was proved that understanding and improving EPC differentiation can constitute a diagnostic and remedial base concept in the diagnosis of ROP.