Abstract: The adsorption amounts of three types of surfactants，i.e.stearic acid（SA），oleic acid（OA），and cetyltrimethylammonium bromide（CTAB），on the surface of bismuth nanoparticles were investigated，in order to select the best surface modifier. Effects of various factors on modification of bismuth nanoparticles with stearic acid were discussed，and optimal modification conditions were obtained as follows：dosage of stearic acid was 10%（relative to thc mass of bismuth powder），pH=5~6，and modification time was 1 h.Under these conditions，the modified bismuth nanoparticles had good wetting and dispersity in liquid paraffin and the powder was changed from hydrophilicity to hydrophobicity.FT-IR and XRD results showed the organic long-chain group of stearic acid grafted onto the surface of bismuth nanoparticles by chemical bonds；the crystal type of bismuth nanoparticles was not changed，but the grain diameter was decreased periodically.

Key words: bismuth nanoparticles, adsorption, stearic acid, surface modification