In this study, seed extracts of cultivated Amaranthus species were tested for haemagglutinating activity. The extracts were prepared from the seeds of 7 Amaranthus cultivars and analyzed against samples from human, rat and dog erythrocytes. To detect haemoagglutination, 5% suspensions of human blood samples of the types A, B and O were prepared. The presence of polyphenols and saponins were determined in the extracts, yielding positive results for polyphenolics compounds. In order to characterize the proteins present in the amaranth extracts, the protein gel electrophoresis technique was applied. All extracts analyzed showed protein activity, and similar protein profile. The extracts reacted strongly with red blood cells (RBCs) from human ABO blood groups. It also reacted with rat and dog RBCs. The hemagglutinating activity was exhibited by the all extracts and the precipitated lectins from all species tested, however, hemolytic activity was not observed. The results obtained from the Amaranthus extracts indicate that it is non-specific for glycosylated antigens of the ABO system. The findings provide essential information for their use as potential hemoclasification reagents in the immunohematology laboratory.