Migration has emerged as a defining socio-economic phenomenon in rural Bihar, shaping livelihoods, demographic patterns, and family structures. The persistent outflow of labor from rural areas to urban and industrial centers across India is driven by factors such as poverty, unemployment, agrarian distress, and environmental vulnerabilities. This research paper examines the relationship between migration and changing family structures in rural Bihar. It explores how migration alters traditional joint family systems, gender roles, intergenerational relations, and social cohesion. The study is based on secondary data from Census reports, NSSO/PLFS data, and scholarly literature. Findings suggest that migration has contributed to the rise of nuclear families, feminization of agriculture, and shifting authority patterns within households. While remittances improve economic conditions, they also create emotional and social gaps. The paper concludes that migration is both an adaptive livelihood strategy and a transformative force reshaping rural family structures, requiring policy interventions to address its socio-cultural consequences.