Background: Positive marital relations are crucial for healthy family functioning, whereas conflict-ridden marital relations are linked to children's adjustment problems. According to the Emotional Security Theory, destructive interparental conflict leads to children's emotional insecurity, impacting their adjustment. Objective: This three-wave longitudinal study examined the temporal associations between preschool children's reactions to interparental conflict, interparental conflict and children's behavioral problems in Japan. Methods: We conducted a longitudinal three-wave study with Japanese parents of children at three time points: aged 3 (Time 1), 4 (Time 2), and 5 (Time 3). Children's reactions to interparental conflict at Time 2 were assessed using the Security in the Marital Subsystem-Parent Report, which includes subscales for overt emotional reactivity, behavioral dysregulation, overt avoidance, and overt involvement. Results: Our findings revealed a positive association between behavioral dysregulation at Time 2 and internalizing problems at Time 3. However, no significant association was found between behavioral dysregulation and externalizing problems. Emotional reactivity was not associated with behavioral problems or interparental conflict. Differences in age ranges across studies may account for the variance in findings. Conclusions: This longitudinal study highlights the importance of focusing on behavioral dysregulation in preschool children as a factor associated with the relationship between interparental conflict and internalizing problems over time. Emotional reactivity may not serve as a reliable indicator of behavioral problems or interparental conflict in Japanese contexts. These findings underscore the need for culturally sensitive approaches in assessing children's responses to interparental conflict and their potential associations with child development over time.