The article analyzes the main principles behind the ontological doctrine of the Church of Jesus Christ of Latter-day Saints, as well as the characteristics of its genesis, development and functioning in a Protestant environment. The work provides a basic definition of ontology as the science of being, determines its conceptual content in the religious dimension and characterizes essential moments of the sacral history of the Universe and mankind from the perspective of Mormonism that are essential for the study of the ontological aspects of this belief system. The research is accompanied by comparative analysis of the ontological doctrine of the Church of Jesus Christ of Latter-day Saints and philosophical systems that have directly or indirectly influenced the Mormons' worldview, including G. Leibniz's monadology, Aristotle's first principles and Plato's theory of ideas. At the same time, the authors identify the specific features of monotheistic ideas in the doctrine of Mormonism and its difference from other monotheistic beliefs. Fundamental ontological categories, such as movement, time, space, spirit and matter are analyzed through the prism of Mormon perception.