The effect supplemental chromium as chromium-methionine (Cr - Met) on performance and physiological responses was investigated in 24 Holstein Dairy calves (first BW 41 ± 1.9) under heat stress as Completely Randomized Design. Treatments were supplementation 0 (C group), 0.02 (L group) and 0.04 (H group) mg of Cr as Cr-Met/kg of BW 0.75 . Before weaning calves received 4 liter whole milk daily and had adlibitum access to a starter concentrate. Throughout after weaning calves had adlibitum access to a starter concentrate and chopped alfalfa. The average of maximum Temperature-Humidity Index throughout the experiment was 76.5 that induced Mild Heat Stress (MHS) to calves. In the fifth week after birth L group had lower rate respiration than C group (p=0.05). In preweaning serum cortisol was lower for H group than C and L group (P=0.04 and P=0.02 respectively), L group had a lower T 4 than C group (P=0.09). In weaning day, H group had a higher serum cortisol and urea than C group (P=0.02 and P=0.06 respectively) and had a higher Insulin to Glucose ratio than L group (P=0.09), C and H groups had a higher serum total protein than L group (P=0.03 and P=0.04 respectively). After weaning L group had a lower rectal temperature and Average Daily Dry Matter Intake than C group (P=0.02 and P=0.06 respectively). In the 21 th days after weaning, groups that received Cr - Met (H+L) had a higher cortisol (P=0.007), lower T 4 (P=0.04), higher T 3 to T 4 ratio (P=0.1) than C group. In Glucose Tolerance Test insulin Area Under the Curve was higher for C than H group at the 0 to 90 and 0 to 120 min after glucose infusion (P=0.07 and P=0.04 respectively). In the conclusion, L level of Cr - Met lower MHS and sudden weaning effects on calves although H level showed higher physiological persistency throughout the experiment and had not disorder influence on performance and physiological responses. در تاریخ 25/6/1387 توسط کمیته تخصصی زیر