Breeder age and oxygen concentrations from 15-21 days of incubation were tested as factors determining on hatching and subsequent performances of broiler at high altitude. Eggs produced by breeders of 31 or 55 weeks of age. All eggs from 2 breeder ages were distributed randomly into 2 hatching cabinets, which were operated at different oxygen concentrations. The 1st cabinet was oxygenated at 25%, whereas, no oxygen added to the 2nd cabinet and called control group. Fertile hatchability was affected by the Oxygen supplementation and flock age interaction. The highest fertile hatchability was obtained when the breeders were 55 weeks of age with adding oxygen but not in breeders at 31 weeks of age. The fertile hatchability was decreased at 55 weeks of age in control group. The late embryo mortality was significantly depressed in embryos from breeders at 55 weeks of age when oxygen added. Chick weights of hatch, 1st and 3rd weeks among groups were not affected by interaction between Oxygen. supplementation and flock age. Feed conversion ratio and mortality were enhanced in chicks obtained from breeders 55 weeks of age when oxygen added. It is concluded that oxygen supplement to the incubators at high altitude improves the fertile hatchability, feed conversion ratio and decreases mortality of chicks obtained from breeder of 55 weeks of age.