Heat stress affects some physiological parameters especially in sheep but how long the animal takes to eliminate  is unclear in the previous studies So, twenty dry-non pregnant Ossimi ewes were used to study the effect of one-day exposure to heat stress on some physiological parameters. Animals were divided equally into two groups (ten each)., The experimental ewes aged 3-4 years old and weighed 35-40 kg, The control group was kept under the shadow till the end of the experiment. The 1^st group was exposed to heat stress for one day on the first day of the experiment. Cortisol, T3, PCV, and HB, were measured in the blood serum. Skin temperature, rectal temperature, and respiratory rate were determined. The results indicated that there was a significant (P < 0.05)   increase in the exposed group in the level of cortisol on the 1^st day of exposure to heat stress and continued till day 45 of the experiment. There was a significant (P < 0.05) difference between groups in the level T3. It was lower in the exposed group compared to control. PCV, HB were significantly decreased in the exposed group from day 0 till day 45. Skin temperature and respiratory rate were significantly increased in the in exposed group on day 0 only. It was clear that there was a latent effect to heat stress on some physiological parameters for Ossimi ewes.