This study describes a graphene-based wireless inline pressure sensor that can be easily inserted between an implanted microdevice and a blood vessel for in vivo blood pressure monitoring. Our wireless pressure sensor is simply composed of a graphene sheet (piezo-resistive sensor) attached on a microfluidic elastic tube and a coil wound up to the tube as a transmitter. The applied pressure inside the tube can be monitored wirelessly by an external receiver coil. We fabricated the sensor system applicable to monitoring the range of typical blood pressure, 10-18 kPa, by designing the sensitivity depending on the stiffness and the thickness of the elastic tube, the turn numbers of the coils, and the distance between the coils. Furthermore, we demonstrated to wirelessly measure the blood-pressure-mimicking pulsed inputs with our sensor that was embedded in a biological tissue. We believe that our wireless inline pressure sensor could be an effective tool for monitoring in vivo implanted medical devices such as microfluidic artificial kidneys.