Abstract: The linen was simply modified with the cationic surfactant trimethylstearylammonium bromide (STAB) in the aqueous solution. The linen was further hot compressed with unsaturated polyester(UPE) in the mold to prepare the linen/UPE composites. The mass fraction of linen was 28wt%. The moisture absorption ratio of linen is improved 30.3% compared with that of unmodified linen, and thus it becomes more hydrophobic. The moisture absorption behavior of the treated linen reinforced UPE (TL1/UPE) is determined to be improved 26% compared with that of the untreated linen reinforced UPE (UL/UPE). And the diffusion coefficient (D) value of the water molecules in TL1/UPE and UL/UPE is determined to be 0.63×10^-2 mm²/h and 1.11×10^-2 mm²/h, respectively. The water molecules diffuses faster in UL/UPE than in TL1/UPE. The impact strength of TL1/UPE is 2.4 times of that of the pure UPE, and thus the brittleness of UPE is dramatically improved. The TGA test shows the thermal stability of the linen/UPE composites can meet most of the utilizing demanding. It is proved that TL1/UPE is concluded to be with improved hygroscopicity, interfacial adhesion and mechanical properties, and it can be a kind of promising biocomposite with excellent comprehensive properties.