Shared decision-making (SDM) has been institutionally recognized as clinically effective by many Western healthcare systems. Nevertheless, it appears culturally unattractive in China, a country that adheres to Confucian familism which strongly prefers collective family decisions. This study examined this conflict and assessed the influence of Confucian familism on SDM in end-of-life (EOL) care for advanced cancer patients. Between August and November 2018, 188 EOL advanced-cancer patients were randomly recruited from 640 cancer hospital medical records at a Tertiary A-level hospital in Shandong province. Eventually, 164 (87.23%) sample patients were included in the statistical analysis after the non-responsive cases (4.79%) and missing value (7.98%) were removed. SDM was measured through SDM-Q-9, and the patient’s siblings were used as indicators of Confucian Familism. Of the 164 patients, the mean SDM score was 38/100; 47.6% were thoroughly unfamiliar with their treatment plans and fell outside the decision-making procedure. Each patient had four siblings on average. Ceteris paribus, more siblings led to lower SDM. Moreover, being 56–65 years old and open-minded were associated with higher SDM, while higher satisfaction of the quality of EOL care yielded lower SDM. In conclusion, Confucian familism weakened patient–clinician SDM in EOL care for advanced cancer patients.