Metal-core piezoelectric fiber (MPF) is a new type of piezoelectric ceramic device with small size, and has great potential to be used as structurally integrated transducers for guided-wave (GW) structural health monitoring. This paper focuses on the use of MPF as ultrasonic Lamb wave receivers. First, the MPF sensor voltage response is derived by coupling the direct piezoelectric effect to the wave strain field excited by circular crested actuator. The obtained theoretical result is validated on an aluminum plate. Furthermore, the experiment that compares the MPF response to Lamb wave with the PZT response is performed. The results show that MPF sensors can be used to sense Lamb waves clearly. In the end, the directivity of MPF response to Lamb waves was investigated, and another experiment is performed to examine the directivity of MPF response to Lamb waves. The result shows that MPF has high directivity, which can be exploited to triangulate the location of an ultrasound source without prior knowledge of the wave velocity in the medium.