This study investigated the effect of mother behavior characteristics and attachment security on infant behavior characteristics. The subjects were 33 infants(aged 30-42 months)and their mothers. Attachment was assessed by using the Attachment Q-set (Waters, 1987). Mother behavior characteristics and infant behavior characteristics were measured through mother-infant interactions using four problem solving tasks that required the mothers and their infants to work together. Mother-infant interactions during problem solving situation were observed with the use of the Teaching Strategies Rating Scale (Erickson, Sroufe, Egeland, 1985). The results of this study showed a significantly positive correlation between mother behavior characteristics and infant behavior characteristics. With Canonical Correlation Analysis, as the mother showed stronger confidence and positively emotional support, infants tended to report higher persistence, more positive experience and affection. Only when attachment security combine with mother behavior characteristics, it has weighty influence on infant behavior characteristics. In other words, the mediating effect of mother behavior characteristics in relationship between attachment security and infant behavior characteristics was found in mother-infant interactions. In Step-Wise Analysis, the mother's confidence to her infant has significant influence on infant's higher persistence, compliance and lower avoidance. Moreover, the mother' emotional support has an effect on infant's higher enthusiasm, affection and lower reliance. Lastly, mother's respecting autonomy to her infant has influence on infant's positive experience about Problem Solving situation.