A manufacturing process needs to be validated before it can manufacture commercial products. The validation study provides assurance of consistent product quality and knowledge of the impact of process parameters on critical quality attributes. Statistical methods play an essential role in process characterization and process validation. In this presentation, we would like to share our review experience in a few process validation studies. In particular, we will talk about the statistical issues in qualification of scale-down model, in design of experiment as well as in identification of design space for both chemical and biological products.