In tropical and subtropical countries like Egypt, sheep breeding faces environmental thermal stress, especially during the summer when air temperature and humidity are very high. Using Microalgae as an alternative feedstuff can significantly improve sheep growth, health and oxidative status. Therefore, this study aimed to evaluate the effect of consuming two different species of microalgae: Spirulina platensis (SP) and Chlorella vulgaris (C. vulgaris) on the following: growth performance, oxidative status, kidney and liver function, serum Glu, proteins and lipids profile and haematological parameters under hot dry environmental conditions. A total of 32 Ossimi male lambs were divided randomly into four equal groups (n = 8), (G1) was fed the control diet, (G2) was supplemented with S. platensis, (G3) was supplemented with a combination between (S. platensis and C. vulgaris) and (G4) was supplemented C. vulgaris. The results of our study revealed that microalgae supplementation significantly (p ≤ 0.05) enhanced lamb's growth, liver and kidney function, levels of serum immunoglobulin IgG, glutathione peroxidase (GPX) and haematological parameters. Moreover, the levels of thyroid hormones and serum proteins profile were significantly increased in all treated lambs compared to the control group. Our research revealed that including microalgae in sheep's feed can enhance their immune system, promote growth and enhance their general health by mitigating the harmful effects of heat and oxidative stress.