The effects of triazinyl stilbene, distyryl-diphenyl, amino coumarin, and triazole fluorescent whitening agents (FWA) on the dye fading and photodegradation in acid dyed silk were evaluated. Dye fading and fiber yellowing after xenon light exposure were instrumentally evaluated phototendering was assessed in terms of loss in breaking strength. Results showed that acid dye type had greater influence on phototendering than did the FWAs.