This work was carried out on ten apparently healthy lactating buffaloes (4-8 years) belonging to a farm in EL-FAYOM province in hot summer months (39-42°C), and fall season. The animals were considered as two groups, the first group (10 animals) were under effect of environmental heat stress and has some reproductive disorders (long postpartum period, unobserved heat, irregular estrous and delayed conception rate). The second group; the control one, were those animals of the first group but in fall season used in their maximum reproductivity and under suitable ambient environment. The clinical examination indicated increase in respiration rate and rectal temperature in the first group than the second one while the rectal examination showed ovarian inactivities in the animals under stress. On the other hand, biochemical serum analysis showed significant decrease in glucose, total proteins and potassium, insignificant decrease in cholesterol but there were significant elevation in urea and sodium concentrations. The serum hormonal assay revealed significant increased in cortisol and progesterone, insignificant decrease in estrogen and observed decrease in both triiodothyronin (T3) and thyroxine (T4) levels. It is concluded that the endocrinological and biochemical alterations indicate that elevated environmental temperature stressed those animals leading to these reproductive disorders.