It has been reported that thermal and non-thermal stressful stimuli early in the development may influence thermoregulation of juvenile or adult animals (Arjona et al., 1990; Soriano and Branco, 2010). Moreover, it is known that hypoxia can induce decreases in body temperature, metabolic rate and thermal preference of several species (Bicego et al., 2007; Tattersall and Milsom, 2009; Branco et al., 2010). To our knowledge, the effect of hypoxia during incubation in thermoregulation of juvenile chicks has not been investigated until now. Thus, we studied the influence of hypoxia at different phases of incubation on the metabolic rate and thermal preference of 8-10-day-old broiler chicks (Gallus domesticus). To this end, three groups of broiler eggs were distributed in a completely randomized design: normoxia for the entire period of incubation (N; 21% O2 during the 21 days), hypoxia during the first week of incubation (HI; 15% O2) and hypoxia during the last week of incubation (HL; 15% O2). After hatching, all the animals were maintained at thermoneutral zone (TNZ) up to the day of experiments. Measurements of oxygen consumption (VO2) were obtained by open-flow respirometry at (29oC), above (34oC) and below (19 and 24oC) TNZ. Thermal preference was assessed in a thermal gradient chamber. In each experiment, 6-8 animals were used per group. Values are means ± S.E.M., and the data were analyzed as a completely design with repeated measurements using the MIXED procedure of SAS version 9.2. VO2 of chicks at TNZ was lower in the HL (24.47 ± 4.33 mL.min-1.kg-1 STPD) than in HI (37.5 ± 5.03 mL.min-1.kg-1 STPD) and N (40.04 ± 4.28 mL.min-1.kg-1 STPD) groups (p< 0.05). Exposure to 19 and 24oC caused increases in VO2 of N and HL, but not HI, animals (p< 0.05). In contrast, no significant change in VO2 of all groups was observed at 34oC. In the thermal gradient, N chicks spent most part of the time (frequency of distribution) at ambient temperatures of 29-31oC and HI and HL at 24-26oC (ANOVA, p< 0.01). Based on the present results, we can conclude that exposure to hypoxia during the first or the last week of incubation interferes with the metabolic rate and thermal preference of 8-10-day-old chicks.