A wireless intracranial pressure (ICP) monitoring system based on the air pressure sensing is proposed in this work. The proposed system is composed of an implantable ICP sensing device and a portable wireless data recorder. The ICP sensing device consists of an air pressure sensor, an ultra-thin air pouch for pressure sensing, and a low-power dedicated system-on-a-chip (SoC) for the data acquisition control and wireless transmission. The SoC consists of a power management unit, a wake-up controller, the sensor interface, a wireless transmitter, and the workflow control logic. The SoC is fabricated in 0.18 μm CMOS technology with a die area of 3.04 mm × 2 mm. Experimental results show that the prototype implantable ICP device has achieved a resolution of 0.2 mmHg and a battery lifetime of 1 week with a 3 V 50 mAh battery. The ICP device has been tested in the liquid environment. The nonlinearity error is less than ±0.4 mmHg for the full measurement range of -20 to +150 mmHg. Compared to the other implantable wireless ICP solutions in the literature, the proposed system alleviates the biocompatibility issue and increases the measurement accuracy.