Carbon nanotubes (CNTs) wrapped by polyacrylamide (PAM) were synthesized through the in situ free-radical polymerization of acrylamide in the presence of the CNTs. Transmission electron microscopy was used to characterize the synthetic CNTs/PAM. This product dissolved easily in water. The effects of the synthetic product as an additive on the load-carrying capacity and antiwear behavior of a water-based fluid were investigated with a four-ball tribotester. The worn surface images of the steel balls were observed by scanning electron microscopy. The results showed that CNTs/PAM at a certain concentration in the base stock effectively raised the load-carrying capacity and antiwear ability. (c) 2007 Wiley Periodicals, Inc.