Recombinant proteins extracted from inclusion body remain in denaturation status. Renaturation in vitro after initial purification is a key step of downstream processing. A common method of renaturation of recombinant proteins is the dilution method. With Bla g 2 as a model protein, the conformational changes of denatured and renatured Bla g 2 were investigated by applying fluorescence spectra. The effects of different urea concentrations, different SDS concentrations and different pH on the fluorescence intensity of renatured protein were also investigated. The reasons for these were studied with the knowledge of molecular structure.