Poly-beta-hydroxyalkanoate (PHA) is the intracellular product of Haloferax mediterranei. In order to gain PHA, H mediterranei cells are disrupted by an ultrasonication, and PHA is then purified by a centrifugal separation. The results of purification are observed by SEM. Most sizes of PHA granules range from 0.2 to 0.8 mu m. The SEM images demonstrate that the ultrasonication is an efficient mode for the cell disruption of H. mediterranei. The Kick's size reduction law is used to describe the mean size variation during an ultrasonication operation. The required energy is in proportional to the size reduction ratio. Based on this size reduction mechanism, the disruption kinetics of H. mediterranei cells is studied and a theoretical model is derived to relate the cell survival fraction, acoustic power, size distribution index, and operation time. This model provides a theoretical method to predict the cell disruption fraction by ultrasonication under various operating conditions with no parameter adjustment. The results show that an increase in acoustic power. or operation time leads to lower survival fraction of cells. Use of this theoretical model, one can choose the optimum acoustic power and operation time to attain a specific cell disruption fraction.