Polymorphs of piperacillin monohydrate were prepared by various sedimentation methods from piperacillin base for the purpose of developing piperacillin preparations for oral use. Solubility and dissolution rate of each form of the polymorphs were compared with each other. It was found that Form IV showed the highest solubility and the fastest dissolution rate among four forms of polymorphs. In general, the solubility and dissolution rate of two amorphous forms, Form IV and II were higher than those of two crystal forms, Form I and III. The apparent dissolution rates in the artificial gastric juice within 60 minutes were 0.65×10^(-6)mole·min^(-1)·㎝^(-2) for Form IV, 0.36×10^(-6)mole·min^(-1)·㎝^(-2) for Form II, 0.30×10^(-6)mole·min^(-1)·㎝^(-2) for Form III and 0.18×10^(-6)mole·min^(-1)·㎝^(-2) for Form I, respectively.