Regular monitoring of blood flow and pressure in vascular reconstructions or grafts would provide early warning of graft failure and improve salvage procedures. Based on biocompatible materials, we have developed a new type of thin, flexible pulsation sensor (FPS) which is wrapped around a graft to monitor blood pressure and flow. The FPS uses carbon black (CB) nanoparticles dispersed in polydimethylsiloxane (PDMS) as a piezoresistive sensor layer, which was encapsulated within structural PDMS layers and connected to stainless steel interconnect leads. Because the FPS is more flexible than natural arteries, veins, and synthetic vascular grafts, it can be wrapped around target conduits at the time of surgery and remain implanted for long-term monitoring. In this study, we analyze strain transduction from a blood vessel and characterize the electrical and mechanical response of CB-PDMS from 0-50% strain. An optimum concentration of 14% CB-PDMS was used to fabricate 300-μm thick FPS devices with elastic modulus under 500 kPa, strain range of over 50%, and gauge factor greater than 5. Sensors were tested in vitro on vascular grafts with flows of 0-1,100 mL/min. In vitro testing showed linear output to pulsatile flows and pressures. Cyclic testing demonstrated robust operation over hundreds of cardiac cycles, with ±2.6 mmHg variation in pressure readout. CB-PDMS composite material showed excellent potential in biologic strain sensing applications where a flexible sensor with large maximum strain range is needed.