The vibration in a developed wet friction system with paper-based material was investigated. As a result, torsional vibration of the input shaft occurred during engagement. In addition, two components of separator plate vibration were observed in the circumferential direction and normal direction of the friction surface. The effects of lubricating oil and surface roughness of the separator plate on friction and vibration characteristics were discussed. Moreover, it was found that separator plate vibration occurred periodically during the stick-slip motion of the input-shaft.