This study investigated the associations among maternal sensitivity, maternal secure base script co-construction skills, and children's secure base behavior during early childhood. Maternal sensitivity and children's secure base behavior were assessed in naturalistic settings among 81 mother-child dyads when the children were approximately 3.5 years old. Maternal co-construction skills were also assessed at that age via a joint mother-child storytelling task. Maternal sensitivity and secure base behavior were assessed again when children (N = 74) were about 5.5 years old. Results indicated that mother sensitivity assessed at the early age was significantly related to maternal co-construction skills. Maternal co-constructive skills in turn were also significantly associated with children's secure base behavior both concurrently and longitudinally. Finally, regression analyses indicated both maternal sensitivity, concurrently at each point in time, and co-construction skills contributed unique and significant information to the prediction of child secure base behavior.