Abstract: Using LED (lightemitting diodes) as light sources, AA (Arbor Acres) broiler’s morphology of testes were compared with the monochromatic light and discuss the internal mechanism.Day-old 48 male broilers were divided into four light treatments (n=12), including red (660 nm), green (560 nm), blue (480 nm) and control white (400-760 nm) by using LEDFeed and water were provided for ad libitum consumption.Light intensity was 15 lx at the height of birds’ heads and scheduled for 23 h of light and 1 h of dark during the experiment. Serum testosterone and thyroid hormone concentration were determined by using radioimmunoassay and testis weight, testis volume, seminiferous tubule area and the percentage of germ cells were measured at 49 days of age. The results showed that testes developments were affected significantly on blue and green light.Body weight, testis weight, testis volume, seminiferous tubule area and the percentage of germ cells in blue and green light groups were significant higher than those of red and white light groups (7.22%-32.37%, P<0.05), and thyroid hormone and testosterone level in blue were higher than those of others (14.36%-26.20%).In conclusion, blue light could be more efficient to stimulate thyroid hormone and testosterone than other monochromatic lights and to affect morphology of testis in broilers.