The present study was conducted to evaluate the rale of thermal conditioning (TC) of broiler eggs during incubation period, and vitamin C (VC) supplementation to drinking water of hatched chicks on their performance and some blood parameters. A total of 300 eggs were assigned randomly to three experimental groups: control and two thermal conditioning groups (TC-7 and TC-14) which were exposed to 39.5±0.5°C for 4h at the 7^th or 14^th day of incubation respectively. After hatching, each group was subdivided into two subgroups a control and VC-supplemented one. Vitamin C was supplied at a level of 1g/liter of drinking water. The experimental was extended for 5 weeks. Growth performance and blood protein were measured. Results showed that live body weight (LBW) was significantly increased at the first week of age, but no differences in LBW were detected at the other ages. However there were an insignificant increase in the final LBW chicks of TC-7 and TC-14. Administration of VC significantly increased LBW of chicks at 4 and 5 weeks of age compared with the control group. No significant effect of TC on Body Weight Gain (BWG) of chicks at different ages, however, VC addition has a significant effect on BWG at the periods from 3-5 weeks of age and for the whole period. Feed intake was significantly affected by TC treatments, where chicks from TC-7group showed an increase than the other groups. Vitamin C addition significantly reduced feed intake of broiler chicks at 4-5 weeks of age and for the whole period. Feed conversion ratio (FCR) was not significantly affected by either TC or VC addition during the the whole period, but there were significant improvement in FCR for TC-7 chick's group at the period from 1-2 wk and for VC-treated chicks at 3-4 weeks of age . There were non significant effects of TC treatment on blood plasma protein fractions, however VC addition significantly increased plasma total protein level. It is concluded that thermal manipulation of broiler eggs at different period of incubation and vitamin C addition for hatched chicks could be used as a practical approach to alleviate the negative impact of heat stress on broiler chicks performance.