A serum albumin fraction is prepared in high yield and purity from plasma and other albumin-containing blood protein fractions by contacting with a resinous polymeric material having a high capacity for adsorption of albumin, heating at 65.degree.-72.degree. C for about 1-4 hours while maintaining a pH of 5.0-5.5, and then selectively eluting the albumin from the resin-protein mixture at a pH of 3.5-4.5. The resinous polymeric materials are diloweralkylaminoloweralkyl-substituted cross-linked dextran polymers.