多瑪斯的自然法思想堪稱為當代最具活力的古典自然法論，他以完整的哲學體系支持其法律理論。尤其在德行倫理學的系統建構中，「法律」中之「自然法」或「自然道德律」作為人性行為的第一原理，且為客觀的外在原理，與「習慣」－尤其是好習慣「德行」－作為人性行為的內在原理，可說是理解與詮釋人性行為及其是非善惡的雙翼。本文主要以《神學大全》中文版第六冊為據，從多瑪斯德行倫理學系統的背景出發，針對「法律」的定義、「自然法律」的定義、「自然道德律」的內容，以及良知、良心、智德與自然道德律之間的關係異同進行解析與釐清。面臨後現代的各項倫理挑戰，最後期待多瑪斯博大精深的自然法思想在教會以及基督徒學者的持續努力下，理論與實踐均得以延續、擴充且加深，並足以回應與指導具體行動與現實生活。

Aquinas's thought of natural law can be reputed to be the most energetic theory of classical natural law in contemporary. His theories of law are supported by his complete system of philosophy. Especially in the construction of his system of virtue ethics, "natural law" or "natural moral law" (the first principle and objective outward principle of human acts) and "habits" (the inward principle of human acts)-especially the "virtue" of good habits-are the two major approaches to understand and interpret human acts along with their right and wrong, good and evil. This article, based on the sixth volume of the Chinese edition of Summa Theologica and setting out from the background of Aquinas's system of virtue ethics, analyzes and clarifies the definition of "law", the definition of "natural law", the content of "natural moral law" along with the similar and distinct relationships among Synderesis, conscience, prudentia and natural moral law. Finally, in face of all the ethical challenges in post-modem days, it is expected that Aquinas's wide-ranging and profound thought of natural law could be continued, expanded and deepened in its theory and practice by the persistent efforts of the Church and the Christian scholars in order to respond to and guide concrete acts and real life.