The accuracy of face recognition systems is significantly affected by the quality of face sample images. Using degraded face sample images can significantly decrease the performance of face recognition systems. There are not many face quality enhancement methods in the research field. Therefore, it is interesting to investigate whether existing image quality enhancement methods can improve the performance of biometric systems for degraded face images. In this paper, we conduct an experiment to apply nine image enhancement methods to a face database, which contains high quality and degraded face sample images. The experimental results show that some of selected enhancement methods can improve face recognition system performance.