Linseed (Linum usitatissimum) is a cereal considered as a functional food because it is rich in dietetic fibers and omega-3 fatty acids. In literature, protein fractionation according to the Osborne classification and antinutritional contents has not been reported. The objective of the present work was classify and quantify proteins fractions (albumins, globulins, prolamins and glutelins), and quantify antinutritional contents, such as protease inhibitors and lectins. Proteins fractions were extracted from defatted linseed flour with different solvents (1:10, w/v) for 90 min at 5 °C. Albumins were extracted in distillated water, globulins in saline solution, prolamins in 70% (v/v) ethanol, acid glutelins in 0.01 M C₂H₄O₂ solution and basic glutelins in 0.075M NaOH solution. Inhibitory assays were performed against trypsin, chymotrypsin, salivary α-amylase and pancreatic α-amylase. One unit of inhibitory (UI) activity was defined as the amount of inhibitor that decreased absorbance by 0.01 at 440 nm or 565nm. Lectins content was obtained by hemagglutination assays using ABO erythrocytes in presence and absence of ions Ca²⁺and Mg²⁺. Albumins was predominant protein fraction (10.6%) followed by basic glutelins (3.2%) and globulins (1.7%). Prolamins and acid glutelins are minor components, with 0.18% and 0.12%, respectively. Antinutritional components were quantified: α-amylase inhibitors were not detected; amount of trypsin inhibitors was 1990UI/g flour and chymotrypsin inhibitors was 930UI/g flour. Lectins were detected in presence of Ca²⁺ in the acid glutelins with 8 HU to A, B and O, and globulins to B and O erythrocytes. Lectins Mg²⁺ dependent were detected in acid glutelins with 4 HU to B and O erythrocytes. The major storage protein in Linseeds, like rice (Oriza sativa), are glutelins and despite of its status as functional food are rich in antinutritional factors principally serine proteinase inhibitors.