The Chinese medical classics Shangham Lun, Jingui Yaolue and Jingui Yuhanjing are regarded as having been written by Zahn Zhongjing in the early part of the third century A.d. However, all current editions of the three works are based on the northern Song edition revised by Lin Yi and other scholars that was first published in 1065 and 1066. Guizhi appears in prescriptions in all three books as an important medicine. Yet whereas in the Chinese Pharmacopoeia (C.P.) Guizhi is defined as the Cinnamomi Ramulus (the whole twig), in the Japanese Pharmacopoeia (J.P.) it is defined as the Cinnamomi Cortex (the bark). The reasons for this difference between China and Japan has not been studied before. The author conducted a historical analysis of the terms and materials used for cinnamomic medicine in China from the third century B.C. to the year 1066, and the following results were obtained. (1) Until the Han period, the drug name Gui was commonly used for products made from the bark (the cork from the bark being removed) of cinnamomic plant. Such products have been excavated from a tomb where they were interred in the second century B.C., and the drug name Guixin was commonly used for them until the Tang period. (2) The terms Gui, Qin, Mugui, Mugui, guirou, Rougui, Guixin, and Guizhi found in medical texts up to the tenth century were all used for the products made from the bark. The Tang government's pharmacopoeia of 659, the Xinxiu Bencao, designates their material plant as either C. cassia or C. obtusifolium. This product primarily corresponds to Cinnamomi cortex, being Keihi in J.P. or Rougui in C.P. (3) The term Jungui was used from the third century B.C. for products in the shape of a bamboo pipe which were made from the bark of cinnamomic plant twig that had been repeatedly rolled up, and which were used as dietary foods or spices. The Xinxiu Bencao designates the material plant as C. burmanni, and the product corresponds to the cinnamon sticks now in use. (4) As to use Guizhi as decoction, we cannot deny the possibility that in the original medical works of Zhongjing there was a prescription by the name of Guizhi Tang. However, there are no examples of the drug name Guizhi until the sixth century, and most prescriptions of Zhongjing that were used around the Tang period employ Guixin or Gui. Because of this, in some prescriptions there has arisen a contradiction in the terminology; for example in Guizhi Tang, Guizhi might be prescribed instead of Guixin. Further, there are also prescriptions named Guixin... Tang. On the other hand, no evidence has been found that the whole twig of cinnamomic plant was used as a drug prior to the eleventh century. Consequently, this indicates an extremely small likelihood that in the time of Zhongjing the drug name Gizhi was employed, or that the whole cinnamomic twig was employed as a drug. (5) In the Taiping Shenghifang which was published in the early part of northern Song period there is, among the prescriptions for Guizhi, and example drawn from the prescriptions of Zhonjing, of the use of a drug named Guizhi, which has the same meaning as Guixin. However, at the time Gixin was a commonly used term.