同本体论（古希腊语：ὁμοούσιος，homoousios），也称为同本质论，基督教术语，主要用于三位一体神学中，用来解释耶稣与上帝之间的关系。这个字由古希腊语：ὁμός（homós，意为相同的），与古希腊语：οὐσία（ousía，意为本质，本体或存在）组成，尼西亚信经中，称耶稣与上帝是homooúsios（同性同体、本体相同、同一本质、同一属性），意思是，他们在本质上完全相同，与上帝是相等的。在第一次尼西亚会议中，基督教会接受这个解释，用来澄清耶稣与上帝的神性。拉丁神学中，将它译为同质论（拉丁语：consubstantialis）。

Homoousian (/ˌhɒmoʊˈuːsiən/ HOM-oh-OO-see-ən; Ancient Greek: ὁμοούσιος, from the Ancient Greek: ὁμός, homós, "same" and Ancient Greek: οὐσία, ousía, "being") is a technical theological term used in discussion of the Christian understanding of God as Trinity. The Nicene Creed describes Jesus as being homooúsios with God the Father — that is, they are equally God. This term, adopted by the First Council of Nicaea, was intended to add clarity to the relationship between Christ and God the Father within the Godhead. The term is rendered "consubstantialis" in Latin and in related terms in other Latin-derived languages which lack a present participle of the verb *to be*. It is one of the cornerstones of theology in Christian churches which adhere to the Nicene Creed.