Fractionation of flax shives into constituent biopolymers and their further conversion into bioproducts represents a significant opportunity for ensuring environmental, social, and economic sustainability. In this work, high molecular weight lignins (HML) and low molecular weight lignins (LML) were extracted from flax shives using pressurized 30% aqueous ethanol (PAE) and isolated with a simplified precipitation method. The HML and LML isolated from flax shives were characterized using multiple techniques including: HPLC analysis for purity; size exclusion chromatography (SEC) for molecular weights; potentiometric non-aqueous titration for functional group determination; and solubility tests.  The highest yield of HML was 13.5g/100g of flax shives, and this was nearly eight times higher than the LML yield. SEC of lignin samples revealed that the molecular weights of HML and LML were ~30,000 and ~8,800 Da, respectively.  HML contained fewer carboxyl groups and more phenolic hydroxyl groups than LML. The higher molecular weight (~30,000 Da) and higher phenolic hydroxyl content of HML makes it an excellent candidate for applications as a polymer in various systems directly or after certain chemical modifications.