本文探討《荀子》與《呂氏春秋》書中「忠」和「忠信」概念之內涵，及其在戰國後期「忠」和「忠信」概念之演變中發揮的角色。戰國中期，「忠」概念受到來自「命運論」、「養生論」，以至稷下學者所提出的政治社會思想的批評。《荀子》和《呂氏春秋》針對這樣的思想脈絡，一方面提倡「忠」概念的價值；另一方面也重新界定了「忠」概念的內涵。在《荀子》「忠」觀的內容中，能顯現他的思想特色者，在於荀子大力提倡作為君德之「忠信」這一點。而在《呂氏春秋》中，作者在引證時將原先描述的「忠臣之悲劇」轉換成「忠臣救國」的故事，試圖勸勉君主一定要聽取「忠言」。與一般印象大不相同，《呂氏春秋》的作者允許「臣下」擁有選擇「效忠」對象之自由，以保持「士」階層之主體性。 This article aims to elucidate some significant aspects in the develop-ment of the Warring states' political thought by means of analyzing the con-cepts of "zho-ng" (Loyalty) and "xin" (Trustworthiness) and their philosophi-cal significance in the Late Warring States thought. In the middle-late War-ring States' socio-political disputes, Daoists and Jixia Masters have critic-ized the value of zhong and xin as ethico-political value. On this criticism Xunzi and the authors of the Lushi chunqiu attempted to restore their value for establishing the worldwide ethical government. Xunzi emphasized their value as one of cardinal virtues for the world-ruler to deliver his love to their subjects. On the other hands, the authors of the Lushi chunqiu defended the value of zhong as the moral ciriteria for hiring most loyal and sincere minis-ters. Nevertheless, in relation with the idea of philial piety, the Lushi chun-qiu regarded the value of zho-ng as subordinate to it, the importance of zhong has not been highlighted as much as in Xunzi's philosophy.