The increased incidence of skin cancer in recent years has resulted in a repeated call for the prevention of UV radiation damage and so investigation on the effects of UV radiation has become more and more important for researchers. In an effort to reduce solar UV radiation exposure, one important method is to use UV-protective textiles. Swimwear fabrics are mostly exposed to sunlight during the summer days, so that it is expected that they provide more UV protection than other textiles. In this study, swimwear fabrics with the same knitting construction and different fiber composition (80% PET+20% /Elastane, 80% PA+20% Elastane) were treated with suitable dyestuffs and UV absorber agents at different concentrations. Then, all the treated swimwear fabrics were tested for UV absorbance (AS/NZS 4399), color fastness to rubbing (EN ISO 105-X12), light fastness (TS 1008 EN ISO 105-B02), color fastness to perspiration (acidic and basic-TS EN ISO 105 E04), color fastness to sea water (EN ISO 105 E02), and color fastness to chlorinated water (EN ISO 105 E03) to evaluate the effect of their treatment parameters (such as UV absorber agent, dye concentration) on the UV protection characteristics of the swimwear fabrics.