The Author has previously made a study on vibration of a cylindrical shell which is immersed in water, and reported the result in this Proceedings. Present report is the outcome of continuation of this study. Here the vibration of an elastic straight bar of circular cross section, which is placed in a water tank of cylindrical form, is studied. From the analytical expression for the vibratory motion of water particles thus set up, the amount of hydraulic force acting on the elastic bar is obtained. For the case in which there exist no end-walls (lids) of the cylindrical tank, it is shown that the frequency of vibration of the bar can be expressed by a simple formula wherein the effect of surrounding water is taken into account, the bar itself being supported at both ends. For the case in which end-walls of the cylindrical tank exist, it becomes a very complicated task to evaluate the frequency of the bar. But, by actual examination of numerical values, it was possible to point out that, as long as the length of the bar is more than about ten times its diameter, the same formula as when there exist no end-walls can be used for estimation of the frequency of vibration of the bar, at least for practical purposes.