To improve the deep coloring effect of PET fabrics, the alkali treated and black dyed PET fabrics were treated with 2 kinds of low refractive compounds such as acrylic resin and silicone resin. The color depth effect of treated PET fabrics was evaluated as lightness(L) change by UV-visible spectrophotometer. As the weight loss of PET fiber treated with alkali increased, the color depth of PET fabrics increased. Lightness(L) of PET fabrics treated with deep coloring agent was lower than that of untreated PET fabrics. The optimum concentration of treated PET with deep coloring agent was 4% o.w.s. The deep coloring effect of PET fabrics treated with silicone resin was higher than one treated with acrylic resin. PET fabrics treated with silicone resin only might be more appropriate process than PET fabrics treated with acrylic and silicone resin for giving deep coloring effect for polyester fabrics.