Composite films of boron-doped nanocrystalline diamond and amorphous carbon (B-doped NCD/a-C) were prepared using a coaxial arc plasma deposition (CAPD) method at an unheated substrate temperature without using any reaction gases. The aim of this study is to indicate that the deposited films can be used as high-performance electrochemical electrode materials. Cyclic voltammetry (CV) measurements of the deposited films showed that they exhibit the unique electrochemical characteristics of diamond crystallites. The 4-nitrophenol (4-NP) aqueous solution, which is a recalcitrant substance found in industrial effluents, was degraded via electrolytic treatment using a batch-type system wherein the deposited films were used as anodes. UV-Vis measurements revealed that part of the molecular structure of the 4-NP changed during this reaction. Furthermore, the total organic carbon (TOC) content in the 4-NP aqueous solution decreased as the electrolytic reaction progressed, implying that the degradation of 4-NP proceeded to yield CO 2 . The results reveal that the B-doped NCD/a-C films prepared using CAPD can be used as high-performance electrochemical electrode materials in industrial water treatment.