The over-expression of recombinant proteins in large amount is important for production of therapeutic proteins and structural study. There are several systems for expression of recombinant proteins. One of the most relevant expression systems is Escherichia coli (E. coli). Although this organism has many advantages, most of recombinant proteins expressed in E. coli hosts form inclusion bodies. For gaining biological activities, these structures should be refolded. Many techniques have been developed for in vitro protein refolding.