Trajectories of children's temperamental reactivity (negative affectivity and surgency) were examined in a community sample of 370 children across the ages of 4 to 7 with hierarchical linear modeling. Children's physiological reactivity (respiratory sinus arrhythmia [RSA]), physiological regulation (Delta RSA), and maternal parenting behavior were included as predictors of children's trajectories of temperamental reactivity. Results indicated that negative affectivity and surgency decreased from 4 to 7 years of age; however, within-person changes in negative affectivity were dependent on levels of baseline RSA and not age. Increases in negative affectivity were also predicted by higher levels of earlier maternal controlling behavior. Decreases in surgency were predicted by higher levels of Delta RSA during mother-child interaction tasks and positive parenting behavior. Baseline RSA and maternal controlling parenting also accounted for interindividual differences in children's negative affectivity at age 7, and gender and children's baseline RSA accounted for interindividual differences in children's surgency at age 7. Overall, these results provide further evidence that parenting behavior and children's RSA influence the changes that occur in children's temperamental reactivity.