Adolescents with higher socioeconomic status (SES) report better mental health. The strength of the association-the "social gradient in adolescent mental health"-varies across countries, with stronger associations in countries with greater income inequality. Country-level meritocratic beliefs (beliefs that people get what they deserve) may also strengthen the social gradient in adolescent mental health; higher SES may be more strongly linked to adolescent's perceptions of capability and respectful treatment. Using data from 11-15 year olds across 30 European countries participating in the 2013/2014 Health Behaviour in School-aged Children study (n = 131,101), multilevel regression models with cross-level interactions examined whether country-level meritocratic beliefs moderated the association between two individual-level indicators of SES, family affluence and perceived family wealth, and three indicators of adolescent mental health (life satisfaction, psychosomatic complaints, and aggressive behavior). For family affluence, in some countries, there was a social gradient in adolescent mental health, but in others the social gradient was absent or reversed. For perceived family wealth, there was a social gradient in adolescent life satisfaction and psychosomatic complaints in all countries. Country-level meritocratic beliefs moderated associations between SES and both life satisfaction and psychosomatic complaints: in countries with stronger meritocratic beliefs associations with family affluence strengthened, while associations with perceived family wealth weakened. Country-level meritocratic beliefs moderate the associations between SES and adolescent mental health, with contrasting results for two different SES measures. Further understanding of the mechanisms connecting meritocratic beliefs, SES, and adolescent mental health is warranted. Copyright © 2020 Society for Adolescent Health and Medicine. Published by Elsevier Inc. All rights reserved.