The study was designed toinvestigate the effect of light schedule on growth performance, carcass traits and blood parameters of broiler chicks. Day-old-Cobb avian 48 broilers were allocated to 4experimental groups, each with 4 replications. All chicks were kept in floor pens. Birds were subjected to four light schedules: continuous light (control), 18 light (L):6 darkness (D), 17 h L: 7h D and 16h L: 8 h D. Scotoperiods were applied twice a night; the first at 7.00 p.m and the second at 5.00 am. Broiler growth performance, carcass traits, selected blood parameters and economic efficiency were estimated.          It was observed that chicks exposed to 18h L: 6h D consumed more feed and had significantly higher body weight gain while feed conversion was unaffected compared with the control groups; the performance of other groups was comparable to that of the controls. Light schedule positively affected the economic efficiency but had no effect on carcass traits, except percent liver which was significantly higher in birds kept under 18h L: 6hD compared with the control ones. Light schedule did not affect plasma total protein or activity of transaminases but significantly affected plasma level of albumin, glucose, cholesterol, T3 or T4. In conclusion, use light schedules, 18 light (L): 6 darkness (D), showed best results for growth performance and Thyroid hormonal without any negative effect on other blood parameters