This research aimed to understand the syncretism in architectural forms of Demak Grand Mosque. The architecture of Demak Grand Mosque was influenced by Islam Kejawen religion syncretism. This was in line with the compromise method applied by the Walisanga to spread Islam in the Java community. The method used in this research was descriptive, analytical and interpretive, elaborated with the concept of acculturation i.e adoption, synergy, and adaptation, and the concept of Islam Kejawen religion syncretism, i.e addition, exchange, and new creation. The results of this research showed that the syncretism in architectural forms of the Demak Grand Mosque, could be traced through the relation of local architecture, i.e Javanese (Kejawen) architecture and Hinduism/Buddhism architecture, with foreign architecture, i.e Nabawi Mosque, Pan-Islamism moeques, modern architecture and colonial architecture. This research was expected to contribute knowledge of the theory about the specific methods to read the syncretism in architecture that was global.