Emotion socialization is a fundamental process for adolescent's psychological functioning, yet multiple socialization agents have rarely been examined simultaneously. We tested emotion regulation (ER) as a mediator and friend supportive emotion socialization as a moderator on the relation between parent unsupportive emotion socialization and adolescent internalizing symptoms. Participants were 132 adolescents (Mage = 16.30 years, 53.0% girls, 80.3% White) and a parent. We used a multi-method (observation, questionnaires) and multi-informant (parent, adolescent) approach. Parent unsupportive emotion socialization was linked to poorer sadness/worry and anger regulation. Friend supportive sadness/worry and anger socialization were related to fewer internalizing symptoms. Regarding moderation effects, at low levels of sadness/worry friend socialization, the link between sadness/worry regulation and internalizing symptoms was strongest, although also significant at medium and high levels of friend support. Both type of emotion and socialization agent are important to consider when understanding associations with internalizing symptoms.