This paper develops its argument in three stages. First, we outline the formation of Chuang Tzu's theory of ch'i. For Chuang Tzu, the conception of ch'i not only underlies and describes the natural process of change, but the spontaneity of ch'i also underlies and suggests his spontaneous approach to cultivation (by non-cultivation). Second, we explore Chang Tsai's claim, ”tai-hsü ji ch'i” (the great emptiness is just ch'i). Finally, we compare Chuang Tzu and Chang Tsai's conceptions of ch'i in the contexts of their cosmologies, approaches to self-cultivation, and views of life and death. Through this three-stage study and comparison of Chuang Tzu and Chang Tsai's conceptions of ch'i, we hope to reveal the rich content of their thought.