Hypothalamic-pituitary-adrenal (HPA) axis activity has been identified as a mechanism through which daily life stress contributes to health problems and racial/ethnic health disparities. Stress-related changes in neuroendocrine function are evident as early as adolescence, but the ways in which promotive cultural factors may also contribute to variation in diurnal HPA activity have received little empirical attention. Grounded in cultural models of resilience, dual dimensions of Latino adolescents' cultural values (ethnic heritage and U.S. mainstream) were examined as promotive and protective factors in relation to their diurnal salivary cortisol patterns using ecological momentary assessment (N = 209; M = 18.10; 64.4% female). Participants provided 5 daily saliva samples for 3 days while completing corresponding electronic diary reports and using time-sensitive compliance devices (track caps, actigraphs). Results from 3-level growth curve models indicated that higher U.S. mainstream cultural values (e.g., self-reliance, competition, material success) were associated with higher average waking cortisol levels and a more rapid rate of diurnal cortisol decline (i.e., "steeper" slope). Regarding situational deviations from the diurnal rhythm (within-person differences), cortisol levels were higher in relation to diary-reported ongoing stress (vs. completed). Accounting for these situational differences in stress timing, a cross-level interaction (i.e., between-person difference in within-person process) indicated that higher perceived stress than usual was associated with lower cortisol levels for adolescents with stronger alignment to Latino ethnic heritage values (e.g., familism, respect, religiosity), compared to relatively higher cortisol levels for those with less alignment to these values. Results were consistent adjusting for participants' sex, immigrant generation, parents' education level, depressive symptoms, medication use, sleep duration, and other self-reported health behaviors. These findings join the growing science of cultural neurobiology by demonstrating the promotive and potentially regulating influence of cultural values in the daily HPA functioning of Latino adolescents.