Lectins are a group of proteins widely distributed in nature, found in higher animals, microorganisms, insects and plants. Plant lectins are defined as proteins which have at least one non-catalytic domain that reversibly bind specific mono or oligosaccharide moieties, and thus mediate molecular level cellular recognition and messaging or other biological role. Research on plant lectins show that some of them may also be involved in plant defense system against plant pathogens and predation. Although their true biological role remains unclear, their specificity towards determined glyco receptors makes them good targets for structural and functional correlation studies. Camptosema ellipticum (Desv.) Burkart is a Papilionoideae subfamily herb found in the São Paulo cerrado and Mato Grosso do Sul wetlands. Camptosemin is a lectin of the Camptosema ellipticum seed cotyledons, which binds lactose. Erythrocyte agglutination inhibition assay was promoted by lactose (25 mM), galactose and sucrose (125 mM). Camptosemin monomer has a MW about 24kDa observed on the SDS-PAGE and mass spectrometry. Its oligomerization state, investigated by fluorescence and circular dichroism, was temperature and pH dependent. Thermal denaturation curve showed the presence of intermediate forms and the total denaturation was achieved above 90 ^oC.