Background: Adolescents experience various emotional, cognitive, and behavioral issues for which there is emerging evidence for mindfulness-based interventions, but these have not been investigated with Indian adolescents. Objectives: To study the impact of mindfulness practices on attention, perceived stress, emotional competence, and mental health among high school adolescents. Method: A single group theme-based 4-week (12 sessions) mindfulness intervention program was conducted on school-going adolescents with a pre-post scale-based assessment design. Results: Thirty-nine out of 45 recruited participants (mean age 15.9 ± 0.56 years; M:F = 2:1) completed the study with high session attendance rates (82.05%–100%). On a paired t-test, there was a significant improvement on the Digit Letter Substitution Test ( p < .001), the Perceived Stress Scale ( p < .001), and three subscales of the Emotional Competencies Scale-Revised ( p < .001–.004). Analysis of non-normal data on the Wilcoxon sign-ranked test revealed significant improvement in the Adequate Depth of Feeling subscale of Emotional Competence ( p < .001) and all subscales of the Strengths and Difficulties Questionnaire-Teacher Version ( p < .001–.048) Conclusion: The results indicate that formal mindfulness-based practices for adolescents have significant psychological benefits. Further randomized controlled effectiveness trials are required to establish effectiveness in the non-clinical adolescent population.