The color depth of PET fabrics treated with colloidal silver and black disperse dye were investigated in this study. Five different add-on levels of the colloidal silver were applied to a polyester microfiber fabric and a polyester regular fiber fabric. Results showed that lightness(L*) and reflectance(%) of PET fabric treated with colloidal silver were lower than those of untreated PET fabrics. Also we investigated the effect of added colloidal silver on washing, sublimation, rubbing, perspiration, and light of treated PET fabric. The increase of color depth and satisfied colorfastness grade were attained by colloidal silver.