A total number of 500 two weeks old sexed chicks from each strain (Inshas and Matrouh) were used to study the effects of early heat stress on productive performance and some physiological and immunological traits. The chicks were divided randomly into five equal experimental groups (100 chicks for each group, 50 male and 50 female chicks). The first group didn't received any treatment and served as control, The second group was exposed to early (6 weeks of age) heat stress without any anti - stress, The third group received the same treatment as the second group with anti -stress, The fourth was exposed to both early (6 weeks of age) and late (12 weeks of age) heat exposure, without anti-stress, The last group received the same treatment as fourth group with anti- stress. The heat stress was for 4 hours / day for 5 consecutive days at 38- 40°c inside the house and the anti-stress was vitamin C (Ascorbic acid) where it was added at level of 3 gm (20% concentration) / liter drinking water during one day before heat exposure until the end of the treatment.  The obtained results could be summarized as following:                                   1- Body weight after treatment for Matrouh was higher significantly (P≤0.05) than Inshas. The     heat exposure affect body weight but the effect was not clear.                               2- At 12 weeks of age the treated group that received vitamin C (Treatment3 and 5) were higher significantly (P≤0.05) than other treated group and control.                                        3- Body weight gain (at 6 weeks of age) in Matrouh strain was higher significantly (P≤0.05)  than Inshas .It take the same trend as body weight. With regard the sex the male body weight gain was higher than female for both strains.                                                     4- At 8 weeks of age, body weight gain was higher in vit. C treated group than others (T3  compared with Treatment1, 2,3,4,5). The same trend was observed at 12 weeks of age.      5- Early heat exposure either with anti stress or not decreased body weight gain significantly (P≤0.05) than other treatments and control. 6- Growth rate was higher significantly (P≤0.05) in male chicks than female at 4,8,12 ages. Also, Inshas strain has higher growth rate than Matrouh strain at all ages.                   7- With regard to humoral Plasma total protein, albumin, globulin, glucose, there are no significant difference at 6and 12 weeks of ages. The differences between sexes and strains are not significant (P≤0.05).                                                                                                    8- With regard to humoral immune response against ND and SRBC's the differences between strains or sexes are not significant (P≤0.05).                                                  9- The group received early and late heat stress with anti - stress (vit. C) has the best value for humoral immunity against ND.                                                           . 10- Geometric mean value for Antibody production showed the same trend, group 5 (received early and late heat stress with anti stress Vit. C) has Large value for both strain and two sexes than the other groups and control.