The effects of hypoxia at increased altitude levels on the cardio-respiratory development of broiler embryos are distinct in comparison with those at sea level. The aim of the study was to investigate the effects of high incubation temperature (H) and oxygen supplementation (O) during hypoxic high altitude (HA) on developmental and physiological traits of embryos and hatching performance of embryonated hatching eggs in broilers at different embryonic stages. A total of 1280 eggs obtained from broiler breeders laid at sea level were used. Eggshell quality characteristics were measured for 20 eggs. The rest of the 1260 eggs were divided into seven incubation condition (IC) groups (180 eggs per group) including a control group at 37.8 degrees C and 21% O-2; O groups, with daily 1 h 23.5% O-2 supplementation at 37.8 degrees C as O0-11, O12-21, and O18-21; H groups at 38.5 degrees C high incubation temperature at 21% O-2 as H0-11, H12-21, and H18-21 from days 0 to 11, 12 to 21, and 18 to 21 of incubation, respectively. All groups were incubated in three different incubators at hypoxic HA. The effect of IC was determined on eggshell temperature, hatching performance, embryo development, right ventricular (RV) to total ventricular (TV) ratio, and blood parameters. The highest egg water loss and embryonic mortality and the lowest hatchability were in the H0-11 group, which depended on increased eggshell temperature during incubation. On day 18 of incubation, due to the decreased egg water loss in the O12-21 and O18-21 groups, there was an increase in hatchability in fertile eggs similar to the middle and late H groups. Towards the end of incubation, embryo/chick weights were not different and RV and TV weights increased in the treated groups, and the RV / TV ratio changed between 15 and 26 %. At hatching, yolk sac weight increased in H0-11 and H12-21 groups. The O groups had the lowest serum tri-iodothyronine (T-3) concentration as distinct from H groups. The serum thyroxine (T-4) concentration increased in the treated groups, dependent on sex of the embryo. Blood hemoglobin concentration of O groups decreased relative to other groups. The hematocrit value was the lowest in the O12-21 and highest in the H12-21 groups. The H and O treatments during pre-hatch hypoxic HA condition can be positively evaluated on physiological traits of embryos after half of incubation depended on the timing of the IC exposure to the hatching eggs obtained from broiler breeders at sea level.