The German scholar G. W. Leibniz was not only an outstanding seventeenth century mathematical logician, he also showed great enthusiasm for studying Chinese culture, especially the Chinese language. Leibniz’s passion for Chinese logography was linked to his interest in the creation of universal characters, and the idea of creating universal characters was influenced by his interest in mathematics. After the publication of Novissima Sinica, he became acquainted with Joachim Bouvet, one of the French Jesuits in China. Bouvet’s figuristic, number-symbolic elucidation of the IChing《易經》strengthened Leibniz’s belief that it was possible to establish a system of characters that could be calculated and deduced just like mathematical or logical signs. The present study focuses on the content of the letters between Leibniz and Bouvet, in which the issues surrounding the I-Ching’s sixty-four hexagrams and the origins of Chinese logography were discussed. It describes how Bouvet’s explanation of the I-Ching served as a mediator through which Leibniz’s ontological perspective, his dyadic progression theory, his study of Chinese characters, and his universal character ideal were all linked together to form a specific epistemological frame. Furthermore, Leibniz’s ontological perspective is compared with the cosmology revealed in the I-Ching. The relationship between the hexagrams, the origins of Chinese logography, and the signs of numbers are also discussed in an effort to determine whether the numerical philosophy of the I-Ching could provide a model for Leibniz’s universal characters.