Introduction: Stress is a determinant factor in thyroid gland functions. A decrease in iodine concentration and thyroid hormones impairs cognitive functions in students. The responsiveness of thyroid hormones to stresses depends on many factors such as the intensity and duration of a particular stressor. This study aimed to examine the effect of mild and short-term social stress on heart rate (HR), blood pressure (BP), triiodothyronine (T3) and iodine concentrations of urine in students. Methods: This controlled before-after study was conducted on 200 students aged 9-12 years (100 girls and 100 boys). The HR and BP of the students were measured and their urine samples were collected before and after the intervention in both stressed and control students. To induce stress, the students were asked to read aloud a text from their own book in front of some audience. Results: In a mixed sample of girls and boys, a significant effect of stress was detected on BP and HR. There was no significant association between the stress and urinary level of T3 and iodine neither in girls nor in boys (and mixed sample). In girls, HR significantly increased in the stressed group while there was no significant connection between stress and BP. In boys, there was a significant difference between stress and control groups in terms of systolic and diastolic BP, but not the HR. Conclusion: Although the stress had a significant sex-specific impact on HR and BP, urinary levels of T3 and iodine were not affected in elementary students.