Abstract: Lignin nanoparticles (NPs) with controlled particle size were prepared by a nanoprecipitation method from acetic acid lignin, where the lignin was not modified particularly by any functional group. The preparation conditions, which could affect the size and feature of lignin NPs, were investigated in detail. The most suitable conditions were stirring rate above 300 r/min, dropping rate 5-40 mL/h, volume ratio of tetrahydrofuran (THF) to H2O 5:100-10:100 and concentration of lignin solution 10-20 g/L. The chemical structure, morphology and physicochemical properties of lignin NPs were characterized by electronic microscope, infrared spectroscopy, X-ray diffraction, elemental analysis, X-ray photoelectron spectroscopy and contact angle measurements, respectively. The results indicated that the average diameter of lignin NPs was 150 nm approximately, and the lignin NPs neither chemically changed on their structures nor formed crystalline particle. The lignin NPs with a hydrophilic core and a hydrophobic surface would enhance their stability.