We propose UV-A Protection Efficiency (APE) as a new valuable index of UV-A protection provided by fabrics, in addition to a UV-B protection factor UPF (Ultraviolet Protection Factor) recommended by CIE. APE was estimated by determining efficiency of apparel white fabrics in suppressing the formation of strand-breakage in plasmid DNA by sparfloxacin-photosensitization with a black light blue (BLB) lamp and solar UV-A radiation. The lower UV-A transmittance of fabrics showed the higher APE. The close inverse correlation between APE and the transmittance of fabrics at 360 nm was demonstrated with the correlation coefficient of −0.86. These findings support the validity of APE as a useful index of UV-A protection by fabrics. For practical use, APE is ranked to three grades depending on tolerated exposure time: APE from 3.5 to 4.5 is good protection, APE from 4.5 to 5.5 is very good protection, APE more than 5.5 is excellent protection. Present study also states that both APE and UPF are the important factors for protecting the ultraviolet radiation by fabrics.