¹Adnan Menderes University, Faculty of Veterinary Medicine, Department of Animal Science, TR-09016 Aydin - TURKEY DOI : 10.9775/kvfd.2016.15723 The aim of this study was to investigate the effects of photoperiod length and light intensity on performance, carcass characteristics and heterophil to lymphocyte ratio in broilers. A total of 272 1 day-old male broiler chicks (Ross 308) were randomly assigned to four treatment groups based on the photoperiod length (23L:1D or increasing duration of light) and light intensity (20 lux vs. a dim, reducing intensity) with four replicates. At 42 d of age, effects of photoperiod length and light intensity on performance traits were not significant. The heterophil/ lymphocyte ratio in 20 lux and dim, reducing light intensity groups were 0.30 and 0.15 (P<0.001), respectively. On the other hand, the effect of light intensity has no influence on heterophil/lymphocyte ratio. Cold and hot carcass weights and whole breast meat and wing weights were found lower in the dim, reducing light intensity group than 20 lux light intensity group. The effects of photoperiod length and light intensity on carcass characteristics were not significant, statistically. In conclusion, it can be said that body weight, feed consumption, feed convertion ratio, whole breast meat and wing weights were increased by providing the increasing photoperiod used with a 20 lux light intensity in broiler breeding. Keywords : Broiler, Carcass, Heterophil/lymphocyte ratio, Light intensity, Performance, Photoperiod