Bioclimatic architecture is currently gaining interest among architect and building designers. In response to this trend, a study using bioclimatic design was conducted in Universitas Diponegoro (UNDIP) Mosque. Modeling simulation using Autodesk Ecotect was carried out to simulate the alternative design of joglo roof. Field measurement were done to validate the difference on the thermal performance between the existing and reccomendation design. Result from field measurement showed the highest room temperature was obtained on the second floor area of the mosque by 28°C. Meanwhile according to the simulation, the bioclimatic roof could decrease the indoor temperature of the mosque around 4.3°C - 5.2°C or to the level of 24.5°C. Moreover, compared to the existing design, the bioclimatic design had higher temperature difference with outdoor temperature by 7.5°C. It means, if an air conditioning system is installed inside the mosque with bioclimatic roof, it would require a lower energy consumption. Thus, the application of bioclimatic roof on the UNDIP Mosque can be a prospective solution to improve its indoor thermal comfort and provide an environmentally friendly design.