There are complex relationships among individual, family, community, and social factors related to breastfeeding. Immigrant mothers, specifically, face several unique challenges to practicing breastfeeding while negotiating these factors within two cultural worlds. Grounded in the theory of planned behavior and the ecological perspective, our qualitative study findings unveil a part of the complex and dynamic process of breastfeeding decision-making among Korean immigrant mothers in the United States. To elicit mothers’ underlying beliefs of attitude and intention toward breastfeeding as immigrants, we conducted in-person interviews with 13 pregnant and postpartum Korean immigrant mothers, ages ranging from 30 to 39. The findings revealed that Korean mothers held positive attitudes toward breastfeeding. However, translation of these positive attitudes toward breastfeeding into actual practice depended on the feasibility of actual breastfeeding by mothers. To overcome several barriers to breastfeeding, such as inadequate milk supply, health concerns, employment status, and the relationship with a firstborn child, many Korean mothers combined breastfeeding with formula feeding. The factors that shaped the development of beliefs and behavioral intentions toward breastfeeding among Korean immigrant mothers included the dynamic family interactions with their children, husbands, mothers, mothers-in-law, and sisters; support from friends and infant care experts; information available through various technology and media; and Korean-specific cultural traditions. Our findings suggest possible directions for future cross-cultural research on breastfeeding within diverse family contexts, and may inform the design of population specific intervention programs.