Objective To examine the effect of Human Amnion-Derived Multipotent Progenitor (AMP) cells and their novel ST266 secretome on neointimal hyperplasia after arterial balloon injury in rats.Material and Methods Sprague-Dawley male rats were randomly divided into four groups (n=7): Control (PBS) group, systemic ST266 group, systemic AMP group and local AMP implant group. Neointimal hyperplasia was induced in the iliac using a 2F Fogarty embolectomy catheter. After surgery, the rats in the ST266 group were treated with 0.1, 0.5, or 1ml ST266 iv daily. In the systemic AMP groups, a single dose (SD) of 0.5 ×106 or 1×106 AMP cells was injected via the inferior vena cava after arterial balloon injury. In local AMP implant groups, 1×106, 5×106, or 20×106 AMP cells were implanted in 300 µl Matrigel (Mtgl) around the iliac artery after balloon injury. The iliac arteries were removed for histologic analysis at 28 days after the surgery. Re-endothelialization index was measured at 10 days after balloon injury.Results ST266 (1 ml) group had a lower level of the Neointima / Neointima+Media ratio (N / N+M) 0.3±0.1 vs 0.5±0.1, p=0.004) and luminal stenosis (LS) percentage (18.2±1.9 % vs 39.2±5.8 %, p=0.008) compared with the control group. Single-dose AMP (1×106) decreased LS compared to the control group (19.5±5.4 % vs 39.2±5.8 %, p=0.033). Significant reduction in N / N+M were found between implanted AMPs (20×106) and the control group (0.4±0.1 vs 0.5±0.1, p=0.003) and the Mtgl-only group (0.5±0.1, p=0.007). Implanted AMPs (20×106) decreased the LS compared with both the control (39.2±5.8 %, p=0.001) and Mtgl-only group (37.5±8.6 %, p=0.016). ST266 (1 ml) significantly increased the re-endothelialization index compared to the control (0.4±0.1 vs 0.1±0.1, p=0.002).Conclusion ST266 and AMP cells reduce neointimal formation and increase the re-endothelialization index after arterial balloon injury. ST266 is potentially a novel, therapeutic agent to prevent vascular restenosis in human.