FeS nanoparticles were prepared by a kind of anaerobic bacteria which was separated from electroplating sludge.The composition,size,morphology,and structure of biological prepared FeS nanoparticles were characterized by means of XRD and SEM.The antifriction behavior of the FeS nanoparticles in 10W40 engine oil was evaluated in MMW1 vertical universal friction and wear testing machine by facetoface contact.Based on the results of SEM and SIMS analysis,the antifriction mechanism of biosynthesized FeS nanoparticles was discussed.The results show that the diameter of biosynthesized FeS nanoparticles with amorphous state was about 50 nm to 100 nm.The friction coefficient of the 10W40 engine oil is reducedby 437%-775% after the addition of FeS nanoparticles.FeS nanoparticles that adsorbed on the surface of the friction pair prevent the direct contact of metal and form an antifriction layer.