High pressure carbon dioxide has been applied to precipitate soy protein. The method is suitable for effective precipitation of soy proteins and prevents local pH overshoot, which usually occurs in case of using mineral acids for the precipitation processes. It was possible to achieve 68.3 wt% of soy protein precipitate using 30 bars of pressurized carbon dioxide, at pH of 5.60 and at constant temperature of 22 +/- 1 degrees C. The rate of mixing was kept at 300 rpm in all experiments, as more froth was noticed while using 400 rpm with a slight rise in temperature. The qualitative analysis using RP-HPLC for soy protein precipitated at 30 bar, showed two totally separated peaks; one for soy protein glycinin with molecular weight of 350 kDa and the second peak was for, soy protein beta-conglycinin with molecular weight 180 kDa: The precipitate at 40 bar showed only one peak for pure soy protein beta-conglycinin, which precipitate later because it has lower molecular weight. This process is considered one of the clean processes leading to highly purified food proteins which need no further treatments to purify the product, to be used in food, non food products and pharmaceutical manufacturing. (c) 2006 Elsevier Ltd. All rights reserved.