Abstract: Different kinds of Ruan are traditional plucked string musical instruments in China. The acoustical properties of Ruan are presented in this paper. Two resonances occur at low frequencies due to the coupling vibrations of top plate, back plate, enclosed air and soundholes. The vibrational modes of Ruan body have been measured and analysed as compared with the vibration of a circular plate. Sound spetra one meter in front of a tenor Ruan are given and the influences of body vibrations are discussed.