A growing urban development pattern can have both positive and negative impacts, one of them is thermal discomfort in the form of heat stress. Heat stress is the maximum condition of the human body to receive heat exposure to various activities. This study aims to analyze thermal comfort in Yogyakarta City based on the Discomfort Index (DI) method. The DI method is commonly used in tropical climates using parameters that contain average air temperature and humidity. DI calculated data consists of secondary data obtained from Geophysics Station Gamping in the 2004 – 2020 and Climatology Station Mlati in 2017 – 2020. The research result of DI obtained that the highest value occurred in the wet moon climate type in April, with 25,63oC. Based on that conditions showed that more than 50% people in the city of Yogyakarta fall into an uncomfortable category with an average index is 24,97oC, which can lead to heat stress. Environmental engineering can be done to decrease the heat stress potential and to improve thermal comfort for Yogyakarta’s urban community, which is application of green transportation, improving people's living behavior, public and private open space, road shade vegetation, application of a vertical garden and a roof garden.