This study explores the persistence and transmission of son preference. Son preference is measured by exploiting a cultural feature, ancestor worship, which emphasizes the importance of having a son in China. To isolate the effect of son preference culture from institutions, a historical experiment, Kuomingtang's (KMT) Retreat to Taiwan, is employed to explore the cultural transmission of son preference. Between 1945 and 1954, KMT resettled approximately one million Chinese in Taiwan, without regard for their cultural background, to meet the party's needs. This bold move resulted in local Taiwanese and Chinese migrants being exposed to groups with vastly different son preference beliefs and behaviors. By combining KMT Retreat and the introduction of sex-selective abortion in 1985, I identify the effect of migrants' ancestor worship on sex selection by using a difference-in-differences framework. The effect is stronger for culturally closer groups and when adopting migrant cultures is less costly. Additionally, I dissect the cultural transmission of son preference in three categories: transmission from migrants to locals, through family, and within migrant communities. I also find migrants' ancestor worship permanently altered individuals' beliefs about ancestors, family, and sons.