Whether mindfulness training (MT) could improve healthy behaviors is unknown. This study sought to determine feasibility and acceptability of integrating MT into school-based health education (primary outcomes) and to explore its possible effects on healthy behaviors (exploratory outcomes). Two high schools in Massachusetts (2014-2015) were randomized to health education plus MT (HE-MT) (one session/week for 8weeks) or to health education plus attention control (HE-AC). Dietary habits (24-h dietary recalls) and moderate-to-vigorous physical activity (MVPA/7-day recalls) were assessed at baseline, end of treatment (EOT), and 6months thereafter. Quantile regression and linear mixed models were used, respectively, to estimate effects on MVPA and dietary outcomes adjusting for confounders. We recruited 53 9th graders (30 HEM, 23 HEAC; average age 14.5, 60% white, 59% female). Retention was 100% (EOT) and 96% (6months); attendance was 96% (both conditions), with moderate-to-high satisfaction ratings. Among students with higher MVPA at baseline, MVPA was higher in HE-MT vs. HE-AC at both EOT (median difference=81min/week, p=0.005) and at 6months (p=0.004). Among males, median MVPA was higher (median difference=99min/week) in HE-MT vs. HEAC at both EOT (p=0.056) and at 6months (p=0.04). No differences were noted in dietary habits. In sum, integrating school-based MT into health education was feasible and acceptable and had promising effects on MVPA among male and more active adolescents. These findings suggest that MT may improve healthy behaviors in adolescents and deserve to be reproduced in larger, rigorous studies.