The objective of this study was to investigate the effect of oxygen supplementation on broiler eggs in a hatchery at high altitude on the growth performance and ascites syndrome of broilers reared at low altitude. The treatment groups were low altitude with no oxygen supplemented in the hatchery (LA-NOX); high altitude with oxygen supplementation in the hatchery (HA-OX); and high altitude with no oxygen supplemented in the hatchery (HA-NOX) group. Growth performance, heart weight, the concentrations of the hormones, T-3, T-4, T3/T4, and and plasma concentrations of haematocrit, haemoglobin, glucose and parameters of ascites syndrome during the growing period were investigated. A total of 243 one-day-old broilers were used for this study. During the growing period, excluding days 7, 28 and 35, oxygen supplementation at high altitude did not affect the live weight of broilers compared with the HA-OX and HA-NOX groups. The cumulative feed consumption was determined to be lower in the LA-NOX group and the same in the HA-OX and HA-NOX groups on the 42nd day. Between 21 and 42 days old, the LA-NOX group had a better feed conversion ratio (FCR) than the HA-OX and HA-NOX groups. Chick weight (CW), yolk sac weight (YSW) and chick heart weight (CHW) were higher in the LA-NOX group than in the HA-OX and HA-NOX groups. At 42 days old, there were no differences between the groups in heart weight, right ventricle weight (RV), left ventricle and septum (LV+Sept.), total ventricle (TV) weight and the RV : TV ratio. The plasma T-3 level was lower in the LA-NOX group than in the HA-OX and HA-NOX groups and T-4 levels were higher in the HA-OX than in the others at 42 days old. The hypoxic conditions that occurred during the embryonic stage - which altered endogenous functions of prenatal chicks and affected several blood parameters, and oxygen supplementation at high altitude - improved chick quality. However, it did not improve subsequent FCR and feed consumption performance of chickens when they were reared at low altitude.