A fast and simple method for screening of ssDNA-breaking photosensitizers was developed using graphene oxide. The ultraviolet light-induced DNA breaks are one of the most harmful DNA damages and cause skin cancer if they are left unrepaired. Since graphene oxide showed relatively strong affinity to the broken DNA than intact DNA, and it quenched fluorescence of the DNA labeling dye effectively, the degree of ultraviolet light-induced broken DNAs could be analyzed by measuring decreased fluorescence after mixing the DNA with graphene oxide. The decrease of fluorescence was highly correlated with the ultraviolet light-irradiating time and concentration of the added drugs. As a result, it was possible to evaluate the efficacy of different ssDNA-breaking photosensitizers in a high-throughput manner. However, conventional methods for the damaged-DNA analysis are time-consuming and require additional manipulations such as purification, radio-labeling, enzymatic digestion, or chemical modification of DNA. The phototoxicity of five drugs such as benzophenone, ketoprofen, indomethacin, naproxen, and norfloxacin was tested using the proposed method. The ssDNA-breaking efficiency of the drugs was well matched with reported efficiency of the tested drugs. In contrast to naked gold nanoparticles, graphene oxide is stably dispersed in the presence of salt, the phototoxicity of the drugs could be successfully tested at a physiological condition using the graphene oxide based method.