Objective To study the effect of monochromatic light on the distribution of retinal ganglion cells in chicks. Methods Sixty One-day-old male broilers were reared under four light treatments, red (660nm), green (560nm), blue (480nm) and white (400-760nm) by using LED (light-emitting diodes) as light sources until the 49th day (n=15). Light intensity was 15 lux at the height of birds’ heads and scheduled for 23hours of light and 1hour of darkness during the entire experiment. The retinas were stained by Nisslstaining and DiIlabeling. The retinal area, cell size and density in ganglion cell layer were estimated by image analysis. Results The retinal area and RGCs’ number in the blue and green light groups were higher than that in the red and white light groups (10.35% and 17.07%, P<0.05). The average cell density of RGCs in the green light group was higher than that in other groups (14.61%, P<0.05). The cell density of RGCs in the green light group was the highest at retinal central area and was higher than that in the blue light group (28.91%, P<0.05). The ratio of CA/NP in the green light group was higher than that in the others (29.71%, P<0.05). The cell size of RGCs in the blue light group was the smallest in central area and the highest in periphery (TP and NP). The ratio of TP/CA in the blue light group was higher than that in the others (26.65%, P<0.05) and there was a significant difference between the others (P<0.05). Conclusion Blue and green lights increased retinal area and RGCs’ number. The decreased amplitude of RGCs’ density gradient in the green light group and the increased amplitude of RGCs’ size gra