Scholarship on Chinese medical history has made considerable progress since last century. However, despite its frequent occurrences in ancient medical and non-medical documents, the word gu, a term associated with diseases, has only been studied in light of the practice of "collecting gu to harm others" in previous scholarship, no attention has been paid to its meaning in the medical study of diseases. Making use of inscriptions on oracle bones, bamboo slips preserved at Tsinghua University, and other pre-Qin documents, this essay aims to (1) explore the meaning of gu in pre-Qin contexts, (2) discuss how ancient people prevented and treated gu, and (3) observe the concepts of illnesses and medical treatments in ancient times.