This thesis presents the development of a wearable ultrasonic sensor to monitor muscle contractions. A flexible and lightweight ultrasonic sensor was constructed using a PVDF film. A numerical simulation model of the sensor, based on Mason’s model, was developed. The performance and frequency characteristics of the developed sensors were investigated. The results of the numerical simulations and experiments show that the developed sensor operates in dual frequencies due to the effect of the non-piezoelectric layers. The ultrasonic signal strength of the sensor with respect to the sensor size was also investigated.Muscle contractions were monitored by the developed sensor. The muscle thickness changes measurement has been used to monitor muscle activities during contractions. The flexibility and lightweight of the sensor allows the sensor to be attached to the body area of interest without restricting the underlying tissue movements, which is not feasible using a conventional handheld ultrasonic probe.