This study was performed to compare the influence of premating supplementation of ascorbic acid(Vit C)andprobiotics (live dried yeast, DY) (Yea-Sacc 1026) (Saccharomyces cerevisiae) on conception rate, thermo-respiratory activities, serum antioxidants, hormonal response and body weight change of heat stressed breeding ewes. The trial was performed on twenty four ewes which were selected and divided into three groups (8 ewes in each) with a completely randomized design. (1) control group: received basal diet without additives, group (2): received basal diet plus (75/mg/kg body weight/day) of vitamin C (Vit C) and group (3): received basal diet plus  live dried yeast (DY) ( 5/g/head/day). The treatments were initiated 2 weeks premating and continued for 4 weeks then after. Blood samples were collected at 2 weeks intervals, starting from the 2^nd week of treatment till the 6^th week of treatment (June-August). All ewes were weighed and observed for thermo-respiratory activity before the beginning of study and at 1 month and 2 month after the treatment. The results revealed that there was a significant (P < 0.01) increase in conception rate in group 2 supplemented with  Vit C as compared with that supplemented with DY or the control group. Vit C and DY treated groups had a significantly (P < 0.01) lower rectal temperature and respiratory rate values as compared with the pre-treatment values and that of the control group. There is a significant increase in Vit C and glutathione -S- transferase levels in the treated groups than those of the control one. Serum level of T3 was elevated (P<0.05) significantly throughout the 2^nd and the 6^th weeks in Vit C group and throughout the 2^nd week in DY group as compared with the control one. Serum cortisol level was significantly (p < 0.05) decreased throughout the trial in Vit C treated group, and only during the 2^nd week in DY treated group. Also, Vit C supplementation lead to a significant (P < 0.05) increase in the body weight as compared with the control one; meanwhile, DY supplementation had a nonsignificant effect on body weight. Results of a premating Vit C supplemented ewes showed a trend towards improving conception rate, body weight, thermo-respiratory activity, antioxidant level, cortisol concentration and thyroid hormones response. So, it could be concluded that premating dietary Vit C supplementation at a level of 75/mg/kg BW/d may offer a thermo-protective role to lessen the destructive effects of heat stress on breeding ewes and may be more economically attractive than DY dietary supplementation under heat stress in summer season.