PET fibers, due to the high refractive index and smooth surface reflect a large amount of light. Thus, the dyeing of these fibers with dark colors, especially black, or high concentrations of dyes for deep shades is difficult. This problem in PET micro fibers is more pronounced due to the high content of light reflection from the high specific surface of these fibers. High surface reflectance of PET micro fibers reveals that the appearance of these fibers is seen paler in comparison to conventional PET fibers and because of this reason it is required more color in order to obtain the same color depth. In recent decades, studies on the surface modification with physical and chemical methods including alkali hydrolyze, using silica micro particles, plasma, corona and UV/Ozone of PET fibers have been done in order to increase the color depth. Most of these studies have focused on creating surface roughness in these fibers to decrease the surface reflection by destructive interference of light. In this study creating surface roughness by laser beams as a new and environmental friendly method was studied in order to increase the color depth in dyeing of PET fabrics. Argon Fluoride Excimer laser beams was used for irradiation of the samples. These samples were prepared for evaluating the effects of laser pulses, irradiation before and after dyeing, increasing the percentage of dyes in dyeing bath and changes in color hue on the color depth in black shade. Color depth of samples was analyzed with studying the CIE color parameters (L*, a*, b*, C*) and reflectance values (RMS, K/S). Changes in the color depth of samples were investigated using surface morphology with SEM images, Crystalinity Index and Crystal size with X-Ray Diffraction, Root Mean Square parameter of surface roughness by Image processing method and dyeing rate with time of half dyeing and percentage exhaustion at equilibrium. The Reflectance of the treated samples revealed that increase in the number of irradiation pulses leads to reduction the reflection in different areas of reflectance spectrum. SEM images demonstrated that his more likely that the increase in depth and height of the surface roughness be the reason for this reduction in the reflection. Increase in Root Mean Square of surface roughness and decrease in L*, confirm this reduction in reflection. Increase the percentage of dyes in dyeing bath results in reducing the reflectance spectral values and chroma of polyester fabric and then increasing in color strength of dyed sample. Increase in dyeing rate and decrease in Crystalinity Index and Crystal Size of PET fibers before dyeing proved that increase in color depth not only depends on surface roughness but also the increase in accessibility of dye molecules in to the porous surface of fibers can. The effects of laser beams on strength and elongation at break, moisture absorption, contact angle and surface chemical structure of the samples were also examined. Contribute to this phenomenon the reduction in the strength and the elongation at break possibly is due to the crack in the fiber and creating a carbon layer on the surface of the fiber after the laser irradiation. Investigation into the surface chemical structure of laser treated PET fabrics by Fourier Transform Infrared Spectroscopy revealed that the conversion of ester groups to carboxylic acid and increase stretching vibration of C-C bond lead to increase in contact angle. Key words : PET fibers, Excimer laser, Color appearance changes, Color depth, Dark shades, Surface morphology, Diffuse reflection.