Objectives : The teaching which states, "Pi is the source of the phlegm and lung is the container of the phlegm" is a sentence that is regarded to have been based on the understanding of the production and container of phlegm based on physiology and pathology of viscera and bowels. However, the author's suspicion that this sentence has not received enough research as to truly understand its meaning has led to further study into this sentence. Methods : Medical book database was searched and historic medical books were reviewed in order to understanding the true meaning of this sentence. First, the meaning of the sentence was pondered upon based on how it was introduced in the original text, and each of the two parts of the sentence were closely analyzed for its relations in order to get a clear meaning of the sentence. Results : The source of this sentence is Bencaogangmu, and it describes the phenomenon of cough in the phlegm appearing more than that from pi and lungs. Later, some disagreements on this sentence developed, claiming that kidney is the source of phlegm whereas stomach is the container. Pi deficiency derives from abnormality in the transportation and transformation of pi, and it originates from kidney deficiency. Thus, kidney can be understood as the origin of phlegm. When phlegm is dispersed all around the body, it's difficult to see the stomach as a container of the phlegm. Conclusions : The pathology of the production and container of phlegm is that deficiency in kidney qi leads to the malfunction of transportation and transformation of pi, and this creates the bodily fluid to become stagnant, making pathological products such as dampness, phlegm, and retained fluid. This can be expressed as "Kidney is the origin of the phlegm, and pi is the source of the phlegm." Here, phlegm is created and stored either when phlegm enters the lungs in the process of pi dissipating into the lungs, or when pi affects the lungs which inhibits the pi movement in the lungs. This is the true meaning of "lung is the container of the phelgm."