孟子論氣，主要著重於人格修養之層次。其說以為，充體之氣為人之存在的生理性基礎，此一生理性基礎雖說必須依從於「心」，必須透過@u的作用加以「成全」，然在平旦未與物接之際，仍存有一絲的良知生發之生機；學者只要當下把握此良知生發之生機，並透過存養、擴充之工夫，即可使之不斯滋長，進而達致「浩然之氣」J的境界。其養氣理論之最大特徵，在於緊扣「心-氣」關係之討論，從中發掘將人之原始生命理性化的可能，並進而融鑄之，使之成為人與宇宙互動的橋樑，從而建立「氣-人性-宇宙」之整體性的生命存在樣態。就歷史發展的角度來說。孟子首次將氣納入心性論的範疇予以考察，並提出完整約有關氣與人格修養之理論，無論就氣概念之發展或心性論之內涵約完善而言，都具有極為重要的意義。

　　　　　Mencius' teachings were derived from Confucius. But in the theory of human nature, Mencius took a further step forward, he definitely insisted that human nature is good. Since man is originally good, the evil is not inborn but due to man's own failures and outside disturbance. The purpose of learning is to "seek for the lost mind." In mencius' mind-heart theory of recovery of original nature, the vital force(chi) have a significant meaning, Mencius said "The will is the leader of the vital force, and the vital force pervades and animates the body. The will is the highest; the vital force come next." Man must cultivate his original vital force, its power is exceedingly great and strong, if nourished by uprightness and not injured, it can fulfill between heaven and earth. The author in this paper try to clarify Mencius' concepts of the air of calm morning(平旦之氣), night air(夜氣), and embodied ch'i(充體之氣). Mencius was the first one to raise ch'i should not be ignored in the history of the development of Confucianism.