To explore patriarchal kinship structure centered on the oldest son across cohorts and time periods, this study compares intergenerational co-residence in the Korean War after Liberation Day (KWALD) cohort and the Korean Baby Boomer (KBB) cohort in 2006 and 2014. Participants are 1,763 KLoSA respondents born between 1945 and 1962 who participated in the Korean Longitudinal Study of Aging survey in both 2006 and 2014 and had living parents at both waves of the survey. Using multiple group analyses the results show that the pattern of the patriarchal kinship structure based on the oldest son status tends to remain in both the KWALD and KBB cohorts. However, in the KBB cohort the family structure based on the oldest son status was weakened in 2014 compared to 2006. These results have implications for the social norms that influence family structure in later life by time period and cohort.