The long period of acculturation among communities on the Island of Java has impacted the exterior architectural characteristics of mosques. Unlike mosques built in the Arab world, the architecture of mosque on Java is firmly influenced by a wide range of cultures. This study attempts to investigate adaptations and adoptions of Hindu-Buddhist, Chinese, and European cultures in the exterior architectural characteristics of mosques on Java Island Indonesia. The main objective of this study is to identify comparative characteristics of the exterior architectural elements of mosques as a result of multicultural adaptation on Java Island Indonesia. The study method is qualitative including academic literature review and direct observation to selected mosques for data collection. Observations of exterior architectural characteristics of the mosque focused on three important elements namely building mass, opening, and decoration. The number of mosques included in the study is nine in total and three for each category, representing Hindu-Buddhist, Chinese, and European Style Mosque. The results show that the exterior architectural characteristic of Hindu-Buddhist Style Mosque is influenced by syncretic religious beliefs that have prevailed for centuries on Java, Chinese-Style Mosque is influenced by Chinese architecture and art with emphasis in traditional symbols and motifs. European-Style Mosque is influenced by renaissance and baroque architecture with an emphasis on symmetry and balance. In conclusion, multicultural adaptations in exterior architectural characteristic of mosque do not change the function and value of mosque as well as eliminate its sacredness as Muslim worshipping place. However, it depicts the symbol of intercultural harmony, diversity, and tolerance among communities on Java Island Indonesia life.