This study aimed to investigate the longitudinal effects of marital conflict and co-parenting on children's executive function difficulties. Data collected from 1,169 children and their parents were analyzed using data from the 5th, 8th, and 11th of the Panel Study on Korean Children. Correlation analysis and structural equation modeling were performed using SPSS 25.0 and AMOS 25.0 programs. Indirect effects were tested through Bootstrapping and Sobel-tests. The results showed that firstly, the marita conflict did not have an effect on children's executive function difficulties. Secondly, marital conflict had an effect on co-parenting. Thirdly, mother's marital conflict had an effect on children's executive function difficulties through mother’s co-parenting. This study confirms that mother's co-parenting is a protective factor in preventing marital conflict and executive function difficulties in early childhood and highlights the importance of improving the quality of mother's co-parenting.