The hydrophobic amino acid residues of a denatured protein molecule tend to react with the particles of the stationary phase of hydrophobic interaction chromatography (STHIC). These hydrophobic interactions prevent the denatured protein molecules from aggregating with each other. The STHIC can provide high enough energy to a denatured protein molecule to make it dehydration and to refold it into its native or various intermediate states. The outcome not only depends on the specific interactions between amino acids, the structure of STHIC, but also depends on the association between the STHIC and mobile phase. The mechanism of protein refolding and the principle of its quality control by HPHIC were also presented. By appropriate selection of the chromatographic condition, several denatured proteins can be refolded and separated simultaneously in a single chromatographic run. A specially designed unit, with diameter much larger than its length, was designed and employed for both laboratory and preparative scales. That unit for the simultaneous renaturation and purification of proteins (USRPP) had the following four functions: to completely remove denaturant, to renature proteins, to separate renatured proteins from impurities, and to easily recycle waste denaturant. The efficiencies of refolding and purification of proteins by the USRPP are almost comparable to a usual long chromatographic column in laboratory. In preparative scale, USRPP can be easily, rapidly, and economically applied requiring a low pressure gradient. As an example, recombinant human interferon-? is employed to elucidate the application of the preparative USRPP.