The pretreatment of ABS (acrylonitrile-butadiene-styrene) plastics prior to metallization has been generally performed with strong acids, such as sulfuric, chromic, or potassium-permanganate acid. However, conventional wet-chemical pretreatment presents inherent environmental and safety problems to consider. In particular, the presence of Cr+6 imposes a serious environmental threat. Therefore, in this study, aspects of pretreatment, using the photocatalytic reaction in TiO2 sol, were investigated as a replacement for wet-chemical pretreatment. Surface characterization, before and after the pretreatment, was examined by X-ray photoelectron spectroscopy and scanning electron microscopy. A copper film was deposited by electroless plating, and the adhesion strength between the deposited film and ABS plastics was evaluated by the cross-cut tape test (ISO 2409). When ABS plastics were pre-treated in TiO2 sol, the adhesion strength was improved to levels obtained using a strong acid solution.