© 2020 by authors, all rights reserved.The thermal comfort conditions of the educational buildings affect students' attention, focus, perception and learning levels. The design of transparent areas is important in the control of solar radiation affecting thermal comfort conditions. The aim of this study is to determine thermal comfort conditions in classrooms with different transparency ratios and to make suggestions for improvements. Classrooms in the same building on the university campus, in the same direction (south) and with different transparency ratios were determined as study areas. Measurements (PMV-PPD) and surveys (AMV-APD) were carried out during a day in heating period. The thermal comfort conditions were evaluated according to the comfort intervals specified in ASHRAE-55 and ISO-7730 standards. The results showed that there were significant differences in thermal comfort between classrooms. If the transparency ratio is more than necessary, it causes discomfort and redundant energy consumption. Suggestions have been made to ensure solar control and thermal comfort conditions.