The surface properties of polypropylene (PP) fibers have an important effect on their reinforcing efficiency in cementitious composites. Two new methods of modifying the surface of subdenier monofilament polypropylene fibers were introduced, as well as the performances of the fiber-reinforced mortar. The results show that the surface modification improved the mechanical performance of the fiber-reinforced mortars, such as compressive strength and flexural strength, and the reinforcing efficiency depends on theadopted method. The enhanced interfacial bonding between treated fibers and the cementitious matrix, compared with that of unmodified fibers, was investigated using scanning electronic microscopy. (C) 2004 Wiley Periodicals, Inc.