For the last decade, due to the popularity of smart devices, flexible pressure sensors that can be used in portable devices are receiving a lot of attention. Lots of fabricating methods have been proposed and intensive research has been conducted. In this thesis, we studied the properties of nanofiber and micro ball composite membranes as sensitive layers of pressure sensors. By adding micron-sized balls to the pure nanofibers, we have dramatically increased the porosity of the membrane. This method improves the sensitivity of the pressure sensor effectively while maintaining membrane stability. Being ultrathin, ultralight, and flexible, the proposed sensors are very suitable for attaching on human body without burden, and hope to be used in future tactile sensor, electrical skin, and wearable healthcare monitoring devices.