This study aimed to investigate intergenerational transmission of paternal attachment and mediation effect of paternal exploratory sensitivity in intergenerational transmission. The subjects in this study were 57 pairs of fathers and 24-month toddlers from dual-earner families in Seoul and Gyeonggi province. Adult Attachment Interview (AAI) and Stranger Situation Procedure (SSP) were administrated to classify paternal attachment representation and toddlers' attachment security. Also, ten-minute play session was included to assess paternal exploratory sensitivity to their children. The results of this study were as follows: First, examining paternal attachment representations through AAI, autonomous type(F) occupied the largest portion by 63.2%, followed by 19.3% with dismissing type(D), 12.2% with preoccupied type(E), and 5.3% with unresolved type(U/d). Conducting SSP to find toddlers' attachment security to their father, results showed that 64.9% were classified as secure type(B), 15.8% as anxious-avoidant type(A), 15.8% as anxious-resistant type(C), and 3.5% as disorganized type(D). Second, the concordance of paternal attachment representation and toddlers' attachment security of four-way classification was 58%, not significant in χ2test. But the concordance of three-way classification and two-way classification were both statistically significant in χ2test (64.9%, 66.7% respectively). Third, the direct effect of paternal attachment representation on toddlers' attachment security was not significant when paternal exploratory sensitivity was controlled. This proved that paternal exploratory sensitivity fully mediated between paternal attachment representation and toddlers' attachment security.