Adjustment of thermal comfort conditions in open urban spaces is now a substantial issue for using these spaces. The creation of an awning is one of the cost-effective strategies for adjusting the thermal comfort conditions of open space. This study examined the difference between thermal comfort indexes in two types of awnings made of straw with and without trees on the Campus of Zabol University located in Sistan in the east of Iran. This study has been conducted based on two widely used PET and UTCI indices of thermal comfort in open space. Therefore, the authors selected and assessed three stations; base station, straw awning without trees and straw awning with trees. The results showed that awning can averagely reduce the PET and UTCI indices up to 3.34 °C and 2.14 °C, respectively. Also, a comparison between stations located beneath the awning indicates that at 12:00 and 15:00, the station beneath the straw curtains with trees has better thermal comfort conditions equal to 1.3 °C and 1.1 °C based on the PET and UTCI indices, respectively compared to the station without trees. This improved situation is explained by the higher humidity in the station with trees, which has somewhat adjusted the thermal comfort conditions rather to the station without trees. The results of this study may be helpful for designers to take a suitable strategy for designing awnings in open urban spaces in similar climates.