This study aimed to investigate the effects of betaine supplementation on some hematological and physiological parameters of Aberdeen Angus cows. Twelve cows were divided randomly into two equal groups (6 cows each) and each group was treated for 150 successive days. All experimental animals were fed 60% of their requirements as a concentrate mixture and the rest of other requirements was covered from wheat strew ad-libitum. In addition to basal diet, animals in experimental group were supplemented with 30 g betaine hydrochloride per day. Air temperature and relative humidity were recorded during the experimental days to calculate the current temperature–humidity index (THI). Blood samples were collected during experimental period from jugular vein. Rectal temperature (RT), pulse rate (PR), respiration rate (RR), skin temperature (ST) and hair temperature (HT) were recorded during the experimental days. The obtained results showed that the average values of THI were between 71.6 to 74.78 at 08:00 am and 77.09 to 83.01 at 02:00 pm during the experimental period which indicates exposure of animals to heat stress. There were no significant differences among groups in WBC, HCT, MCV, MCH, MCHC and PLT. Moreover, RBC and HGB was higher (P < 0.05) in betaine group than control. adding betaine had no significant decrease in RR, ST, HT and ET. While, significant decrease in RT and PR was observed at 02:00 pm of experimental animal. It is concluded that betaine may be improved some hematological parameters and thermoregulatory responses of Aberdeen Angus cows under New Valley arid areas.