The phenomenon of lubricant cavitation in hydrodynamic bearings and its detrimental effects have been documented in many literatures. Collapse of vapor cavitation bubbles may cause erosion wear that limits the life of the bearings. The ability to detect the occurrence of vapor cavitation using a well established condition monitoring technique is essential for the equipment operator. An experiment was conducted to investigate the vibration characteristics of vapor cavitation in steadily loaded plain journal bearings. Vibration data were collected from the bearings operating under the influence of vapor cavitation. It is shown that, vapor cavitation exhibits distinct characteristics on the vibration plots. Low amplitude, forward and reverse 0.063X frequency components, and a series of harmonics with frequencies lower than 0.5X, are observed on the full spectrum. A unique waveform with the positive peak amplitude fluctuating above and below the zero axis line is also observed.