A soy protein product having a protein content of at least about 60 wt % (N×6.25) d.b., preferably a soy protein isolate having a protein content of at least about 90 wt % (N×6.25) d.b., is prepared from a soy protein source material by extraction of the soy protein source material with an aqueous calcium salt solution, preferably calcium chloride solution, to cause solubilization of soy protein from the protein source and to form an aqueous soy protein solution, separating the aqueous soy protein solution from residual soy protein source, concentrating the aqueous soy protein solution while maintaining the ionic strength substantially constant by using a selective membrane technique, optionally diafiltering the concentrated soy protein solution, and drying the concentrated and optionally diafiltered soy protein solution.