The purpose of this study is to investigate the relative effects of socio-demographic and work-family related variables and marital and generational relationship variables on the family strength of middle-aged dual-income families. The subjects of this study were 341 middle-aged dual-income families' males and females among 10,912 respondents of the Family Situation Survey of the Ministry of Gender Equality and Family in 2015. Collected data were analyzed using the t-test, cross-tabulation analysis, correlation analysis, and hierarchical regression analysis using SPSS 23.0 software. The results were as follows. First, in both males and females, family strength increased with increasing monthly income, satisfaction with communication with spouse, and intimacy with adolescent children. Second, family strength increased with decreasing work and family conflict only for females. Third, the variable with the greatest impact on family strength was communication satisfaction with spouse for males and monthly income for females. These results show that monthly income, work and family conflict, communication satisfaction with spouse, and intimacy with adolescent children are major variables that affect family strength. This study is meaningful in that it provides foundational data for developing various programs that improve family strength by exploring such variables related to family strength in middle-aged, dual-income families.