The mosque is generally designed with many ventilation openings to incorporate natural penghawaan into the building with the intention to lower the temperature inside. Mosque General Sudirman is a mosque with window openings on each side. This study aims to determine how the influence of openings on thermal performance at runang in the mosque. The method used is descriptive evaluative with quantitative approach. Measurements are made by measuring air temperature, surface temperature and wind speed. Measurements were carried out for 3 days from 09:00 to 17:00 hours by using experimental simulations on openings. From the conclusion obtained that the influence of openings to the decrease in air temperature inside is not significant. The highest temperature drop was in the comparison of experimental open-window experiments on the 2nd and 3rd floors of 1.18 oC.