BACKGROUND : Palliative care was a priority issue in the Cancer Control Act enacted in 2007 in Japan, and this has resulted in efforts being made toward educational goals in clinical settings. An investigation of how descriptions of palliative care for the treatment of cancer have changed in clinical practice guidelines (CPGs) could be expected to provide a better understanding of palliative care-related decision-making. This study aimed to identify trends in descriptions of palliative care in cancer CPGs in Japan before and after enactment of the Cancer Control Act. METHODS : Content analysis was used to count the lines in all relevant CPGs. We then compared the number of lines and the proportion of descriptions mentioning palliative care at two time points: the first survey (selection period: February to June 2007) and the second survey (selection period: February to December 2015). Descriptions from the CPGs were independently selected from the Toho University Medical Media Center and Medical Information Network Distribution Service databases, and subsequently reviewed, by two investigators. RESULTS : Descriptions were analyzed for 10 types of cancer. The proportion of descriptions in the first survey (4.4%; 933/21,344 lines) was similar to that in the second survey (4.5%; 1325/29,269 lines). CONCLUSIONS : After the enactment of the Cancer Control Act, an increase was observed in the number, but not in the proportion, of palliative care descriptions in Japanese cancer CPGs. In the future, CPGs can be expected to play a major role in helping cancer patients to incorporate palliative care more smoothly.