Uncontrolled hemorrhage resulting from trauma or accidents can be life‑threatening, highlighting the need for rapid and effective hemostatic agents. In this study, a starch-based powder-type hemostatic agent containing polyphosphate was developed. Polyphosphate-modified starch (PMS) was prepared by introducing free amine groups, enabling binding with phosphate. The chemical structure of PMS was confirmed using FT-IR, XPS, and ³¹P NMR. Among the prepared formulations, PMS-1 containing 1 wt% polyphosphate exhibited the highest hemostatic performance. Biocompatibility was verified by an MTT assay. In vivo hemostasis experiments using a Sprague–Dawley rat hemorrhage model showed that PMS-1 achieved hemostasis approximately 40% faster than native starch and reduced blood loss by more than 70%. These results suggest that polyphosphate-modified starch is a promising candidate for rapid hemorrhage control.