Wave attenuation in rock masses is mainly due to the existence of rock joints. A large amount of research has been performed to investigate the effects of closed and open rock joints on wave propagation and attenuation. However, few attentions have been paid to the interaction between open rock joints filled with fluid and wave propagation. In this study, a series of ultrasonic tests were conducted to experimentally study ultrasonic P-wave propagation across rock with single water-filled joints. We found that both of water volume content in the joint and the joint thickness have significant influences on ultrasonic compressional wave propagation through rock masses. Specifically, decreases in wave attenuation and wave slowness were observed with the increasing water content. By contrast, wave attenuation and wave slowness increased as the joint thickness was enlarged. These findings would make contributions to further understanding of wave propagation and attenuation through rock with fluid-filled joints.