OBJECTIVE: Emotion dysregulation has been suggested to be a potent risk factor for multiple psychiatric conditions. Altered amygdala-prefrontal cortex (PFC) connectivity has been consistently linked to emotion dysregulation. Recent data indicate that amygdala-PFC functional connectivity undergoes a prolonged period of development, with amygdala reactivity during early childhood potentially shaping this unfolding process. Little is known about the relationships between amygdala-PFC functional connectivity, amygdala reactivity, and emotion regulation during early childhood. This information is likely critical for understanding early emotion dysregulation as a transdiagnostic risk factor for psychopathology. The current study examined the relationships between amygdala functional connectivity, amygdala reactivity, and emotion regulation in preschoolers. METHOD: A total of 66 medication-naive 4- to 6-year-olds participated in a study where resting-state functional magnetic resonance imaging (rs-fMRI) and parent-reported child emotion regulation ability data were collected. fMRI data collected during a face viewing task was also available for 24 children. RESULTS: Right amygdala-medial PFC (mPFC) functional connectivity was positively associated with child emotion regulation ability and negatively associated with child negative affect and right amygdala reactivity to facial expressions of emotion. Right amygdala-mPFC functional connectivity also statistically mediated the relationship between heightened right amygdala reactivity and elevated child negative affect. CONCLUSION: Study findings suggest that amygdala-mPFC functional connectivity during early childhood, and its relationships with amygdala reactivity and emotion regulation during this highly sensitive developmental period, may play an important role in early emotional development. These results inform the neurodevelopmental biology of emotion regulation and its potential relationship with risk for psychopathology.