By means of a high-sensitive fiber-optic sensor based on optical beam deflection, the oscillating property of a laser-induced cavitation bubble in the vicinity of an aluminum target in water is investigated in detail. The characteristic waveforms induced by a cavity during the two oscillating cycles are presented and the corresponding maximum and minimum radii are determined. Furthermore, the variations of the gas content in a cavity at each oscillation are estimated according to the bubble-collapsing theory. The experimental results are shown that the less the remained gas in a cavity, the more violent the cavity contracts, the smaller the corresponding minimum bubble radii and the shorter the oscillating durations are.