Ultraviolet (UV) irradiation induces helix distorting photolesions such as cyclobutane pyrimidine dimers (CPD) and pyrimidine-pyrimidone (6-4) photoproducts (6-4PP) which threaten genomic integrity if unrepaired. In mammals, nucleotide excision repair (NER) is the only pathway that removes UV-induced DNA damages. Here we describe DNA slot blot repair assay for quantitative detection of NER activity using DNA damage specific antibodies such as anti-CPD and anti-6-4PP. Briefly, genomic DNA irradiated with UV was isolated from cells, and the genomic DNA was vacuum-transferred to a nitrocellulose membrane using a Bio-Dot SF microfiltration apparatus (Bio-Rad). A monoclonal antibody that recognizes CPD or 6-4PP was applied to detect the remaining amount of photolesions in the genomic DNA. For loading control of even loading, DNA onto the membrane can be further analyzed by SYBR-gold staining.