Refolding of reduced and denatured protein in vitro has been an important issue for both basic research and applied biotechnology, Refolding at low protein concentration requires large volumes of refolding buffer. Diafiltration method is useful to control the denaturant and red/ox reagents in the refolding solution, We constructed a refolding procedure for high concentrations of reduced and denatured lysozyme of about 10 mg/ml (700 muM) on linear reduction of urea concentration in diafiltration, 0.8 mM cystine and 8 mM cysteine under nitrogen at 2 atm, This method can obtain about 90% refolding yield at 700 muM and almost 100% in 350 muM lysozyme, The refolding yields during the diafiltration can be simulated using the competitive reaction between the refolding and aggregation. In the red/ox control with cysteine and cystine, a rate order of aggregation reaction of near 2 is obtained.