Synthetic polymeric flocculants are used extensively for wastewater remediation, soil stabilization, and reduction in water leakage from unlined canals. Sources of highly active, inexpensive, renewable flocculants are needed to replace synthetic flocculants. High kaolin flocculant activity was documented for bovine blood (BB) and blood plasma with several anticoagulant treatments. BB serum also had high flocculant activity. To address the hypothesis that some blood proteins have strong flocculating activity, the BB proteins were separated by SEC. Then, the major proteins of the flocculant-active fractions were separated by SDS-PAGE. Identity of the major protein components was determined by tryptic digestion and peptide analysis by MALDI TOF MS. The sequence of selected peptides was confirmed using TOF/TOF-MS/MS fragmentation. Hemoglobin dimer (subunits alpha and beta) was identified as the major protein component of the active fraction in BB; its high flocculation activity was confirmed by testing a commercial sample of hemoglobin. In the same manner, three proteins from blood plasma (fibrinogen, gamma-globulin, alpha-2-macroglobulin) were found to be highly active flocculants, but bovine serum albumin, alpha-globulin, and beta-globulin were not flocculants. On a mass basis, hemoglobin, gamma-globulin, alpha-2-macroglobulin were as effective as anionic polyacrylamide (PAM), a widely used synthetic flocculant. The blood proteins acted faster than PAM, and unlike PAM, the blood proteins flocculants did not require calcium salts for their activity.