Background and Aim: The primary energy for speech production is prepared by breathing flow. As there was no index for the maximum phonation time(MPT) to compare normal and speech disordered speakers in Iran, the purpose of this study was to establish this standard for guidance school students in Tehran. 
Materials and Methods: This cross-sectional study was performed on 576 guidance students from 1^st, 5^th, 8^th, 10^th, 15^th and 19^th educational regions. Each student made an usual inhalation and produced the /a/ for three times with the maximum strength but in a way that he/she didn&apost feel tension on his/her neck or larynx. The maximum time was recorded as the maximum phonation time.
Results: The results of this research revealed that girls`s MPT in all regions was 15.3, 16.7, and 17.16 seconds and the boys` was 15.41, 16.7 and 17.01 seconds and all students` 15.36, 16.17 and 17.08 seconds in order of their grades. There was significant difference between first and third grade mean MPT (p=0.003).
Conclusion: The result of this study indicates that, as the students age increases their MPT increase, too. Also, boys` MPT was more than girls` in first and second grades however, in third grade the girls` MPT was more.