Child-mother attachment security, assessed via a modified Strange Situation procedure (Cassidy & Marvin, with the MacArthur Attachment Working Group, 1992), and parent-reported child proneness to anger were examined as correlates of observed child behavior toward mothers during a series of interactive tasks (N = 120, 60 girls). Controlling for maternal sensitivity and child gender and expressive language ability, greater attachment security, and lower levels of anger proneness were related to more child responsiveness to maternal requests and suggestions during play and snack sessions. As hypothesized, anger proneness also moderated several security-behavior associations. Greater attachment security was related to (a) more committed compliance during clean-up and snack-delay tasks for children high on anger proneness, (b) more self-assertiveness during play and snack for children moderate or high on anger proneness, and (c) more help-seeking during play and snack for children moderate or low on anger proneness. Findings further our understanding of the behavioral correlates of child-mother attachment security assessed during late toddlerhood via the Cassidy-Marvin system and underscore child anger proneness as a moderator of attachment-related differences in child behavior during this developmental period.