本文的目的在於釐清「忠」和其複合詞「忠信」概念的內涵在中國古代思想史中的演變及其思想史上的意義。一般而言，過去對中國古代「忠」的概念的研究大體上都認為，戰國時期所進行的君主集權和官僚制度的形成，促成原來「真心」義的「忠」字變成「為君效勞」義的「忠」字之變遷。反之，本文經過《國語》和《春秋左傳》、中山王陵Ｘ器銘文、以及新出土的「郭店楚簡」<忠信之道>和<魯穆公問子思>中的「忠」字變用例之分析，乃試圖論證，春秋到戰國的社會變化和新的國家與社會秩序之形成，應該首先促進了認同社稷之主張，因而從春秋到戰國時期之「忠」和「忠信」之意涵原來就與政治意義息息相關。也就是說，「忠」概念之核心意涵乃係能貢獻國家社稷的繁榮和安寧之行為，以及其實踐者的「誠懇」之心態。 This article aims to shed new light on the inquiry into the role and the significance of the concept of loyalty (zhong 忠) and trustworthiness (xin 信) in early Chinese political thought by analyzing their usages in Warring States Bronze inscriptions and the Guodian Chu bamboo text, and also in the early Chinese literal texts such as the Guoyu and the Zuozhuan. Previously, scholars considered that the original meaning of the concept of zhong meant "sincerity" and that it was used in small communal relationship such as between friends; also, it has been assumed that this concept was used in the development of Chinese state and bureaucratic system and that its main meaning has been changed into "loyalty toward ruler." The author attempts to show that the term zhongxin from its early use (i.e., during the Spring and Autumn period) contained the meaning of loyalty, and that the content of sincerity represented its later conceptual development (i.e., from the late Spring and Autumn period and later). Yet, in its early use, the objective of loyalty did not point to any individuals but instead to the state to which an individual belonged. The thinkers and political figures before the mid-Warring States period even argued that the possession of zhongxin was imperative for any state to survive. This implies that the concept of zhongxin was probably one of the most important values in early Chinese political thought, even before other main ethical and social ideas were proposed by the Confucians of Warring States.