This paper presents a 0.9m long capacitive force sensor for a catheter integration, which measures a contact force to inner vessel wall or organs with a resolution of 0.5gf. The force sensor is implemented with a thin flexible printed circuit board (FPCB) encapsulated by a force sensitive medium, multilayer polydimethylsiloxane (PDMS). The parasitic capacitance (CP) inherent in long catheters significantly degrades the sensing accuracy of capacitive force sensors. To account for this, this work proposes a sensor interface with CP canceller. By removing the 348pF (91.5%) of CP with the CP canceller, the capacitive force sensor achieves a capacitance resolution of 16aF equivalent to a force error of 0.5gf, which is a 10× improvement compared to the conventional sensor interface. The proposed force sensor offers great potential for real-time force monitoring of cardiovascular surgery.