A mini-invasive system for long-term bladder urine pressure measurement system is presented. Not only is the design cost reduced, but also the reliability is enhanced by using a 1-atm canceling sensing instrumentation amplifier (IA). Because the urine pressure inside the bladder does not vary drastically, both the sleeping and working modes are required in order to save the battery power for long-term observation. The IA amplifies the signal sensed by the pressure sensor, which is then fed into the following analog-to-digital converter. Owing to the intrinsic 1-atm pressure existing inside the bladder, the IA must be able to cancel such a pressure from the signal picked up by the pressure sensor to keep the required linearity and the resolution for pressure measurement of the bladder urine. The pressure range of the proposed system is found out to be 14.7~19.7 Psi, which covers the range of all of the known unusual bladder syndromes or complications.