BACKGROUND: Family history of breast cancer and social networks were found to have an influential effect on women's cancer knowledge and screening practices. There is a scarcity of studies in this area among Asian populations. OBJECTIVE: This study aimed to explore the effect of family history and knowing a friend with breast cancer on Chinese and Korean women's knowledge of breast cancer and screening practices. METHODS: A convenience sample of 742 women, comprising 493 and 249 Chinese and Korean women, respectively, was recruited. Data were collected by the Chinese and Korean version of the Breast Cancer Screening Beliefs Questionnaire. Multivariable linear regression was performed to answer the research question. RESULTS: Korean women with neither family history nor a friend history had significantly higher scores in all 3 subscales of the BCBSQ compared with their Chinese counterparts. In contrast, no significant differences were found between the 2 cohorts in women who have either family history or a friend history. Comparing within the Chinese cohort, women with a friend history obtained a significantly higher score in all 3 subscales of BCBSQ than those without a friend history. Similar significant association was found between having a friend history and screening practices in both cohorts. CONCLUSION: Knowing a friend with breast cancer is an influential factor that impacts women's cancer knowledge and screening practices. IMPLICATIONS FOR PRACTICE: The concept of peer influence should be incorporated into the design of breast cancer awareness and screening promotion programs for women from these cultural backgrounds.