This study presents a tiny pressure sensor which is used to measure the Intracranial Pressure (ICP). The sensor is based on the piezoresistive effect. The piezoresistive pressure sensor is simulated and designed by using nonlinear programming optimizing and Finite Element Analysis (FEA) tools. Two kinds of sensor sizes are designed in the case of childhood and adult. The sensors are fabricated by Microelectro Mechanical Systems (MEMS) process. The test results yield sensitivities of 1.033 $\mathrm{\times }$10 ${}^{\mathrm{-}\mathrm{2}}$ mV/kPa for the childhood type detection and 1.257 $\mathrm{\times }$10 ${}^{\mathrm{-}\mathrm{2}}$ mV/kPa for the adult detection with sensor chip sizes of 0.40 $\mathrm{\times }$0.40 mm ${}^{\mathrm{2}}$ and 0.50 $\mathrm{\times }$0.50 mm ${}^{\mathrm{2}}$, respectively. A novel method for measuring ICP is proposed because of the tiny sizes. Furthermore, relative errors for sensitivity of pressure sensors are limited within 4.76%. Minimum Detectable Pressure (MDP) reaches 128.4 Pa in average.