In his religious work, Ricci published a book known to the West as Secure Treatise on God, or The True Idea of God.
這部書在明萬曆卅五年（西元一六○七年）開始用義大利文撰寫，費時三年完成。原稿經耶穌會金尼閣神父在一六一四年帶到羅馬，分別以拉丁文、法文、西班牙文、義大利文、英文等相繼出版問世。