Surface modification of acrylonitrile-butadiene copolymer (NBR) vulcanizates by treatment with an iodine solution results in a significant decrease in the coefficient of friction. The effect of modification is attributed to formation of a thin surface layer, incorporating iodine species, which has a higher modulus than the bulk material. The surface layer also has an increased roughness which, combined with the increased local stiffness, causes the reduction in friction. These factors overcome an observed increase in the surface energy after modification, which would act to increase the friction. NBR subjected to iodination kept its bulk elasticity, which plays an important part in the mechanism of deformation of the elastomer under conditions of friction, and ensures that the modified NBR retains its properties in engineering applications. The durability of the surface modification is attributed to interactions between iodine and nitrile groups from the acrylonitrile monomer units.