This study examined the associations between maternal scaffolding and toddlers' active joint engagement during play and whether toddlers' temperamental activity moderates those associations. Korean mother-toddler dyads (N = 106) participated in semistructured free play. Maternal scaffolding, toddlers' joint engagement, and physical activity level were videotaped for 15 min, and the toddlers' temperamental activity was reported by their mothers. In a hierarchical multiple regression analysis, we found positive effects of maternal scaffolding on toddlers' joint engagement during play. Maternal scaffolding was more positively associated with joint engagement among temperamentally low active toddlers than among temperamentally high active toddlers. We did not find main effects of maternal scaffolding on toddlers' physical activity level during play but found significant moderating effects of toddlers' temperamental activity on the associations. Maternal scaffolding was negatively associated with the physical activity level of temperamentally high active toddlers. The implications of this study for future research and practice are discussed.