Adult sibling (AS) relationships are seen as mutual support and sharing in all areas of life among those with their own families. The relationships hold a significant meaning in every person’s life, serving as a source of social capital and psychological support and contributing to personality orientation. A prevailing trend is that the more developed the society is, the less close the AS relationship is due to the increased spatial mobility. Whether this occurs in Vietnam amid industrialization and modernization is an intriguing question. Identifying the characteristics of AS relationships and their role in the development of each family can provide a valuable contribution to amending policies on building and fostering Vietnamese families towards prosperity, progressiveness, happiness and civilization. Drawing on the analysis and synthesis of research documents, the article presents some initial findings about AS relationships in Vietnam, including economic- material aspect, sharing obligations and rights in extended families, and other emotional activities. Studies reveal that adult sibling relationships in Vietnam remain cohesive, reflecting the continuation of traditional cultural values such as affection, love, tolerance, and mutual assistance beside some negative aspects. Building on the research findings, the article raises several concerning issues regarding AS relationships to fortify Vietnamese families.Adult sibling (AS) relationships are seen as mutual support and sharing in all areas of life among those with their own families. The relationships hold a significant meaning in every person’s life, serving as a source of social capital and psychological support and contributing to personality orientation. A prevailing trend is that the more developed the society is, the less close the AS relationship is due to the increased spatial mobility. Whether this occurs in Vietnam amid industrialization and modernization is an intriguing question. Identifying the characteristics of AS relationships and their role in the development of each family can provide a valuable contribution to amending policies on building and fostering Vietnamese families towards prosperity, progressiveness, happiness and civilization. Drawing on the analysis and synthesis of research documents, the article presents some initial findings about AS relationships in Vietnam, including economic- material aspect, sharing obligations and rights in extended families, and other emotional activities. Studies reveal that adult sibling relationships in Vietnam remain cohesive, reflecting the continuation of traditional cultural values such as affection, love, tolerance, and mutual assistance beside some negative aspects. Building on the research findings, the article raises several concerning issues regarding AS relationships to fortify Vietnamese families.