This experimental study aimed to investigate the effects of the Mindfulness Program (MP) on high school students' perceived stress, mindfulness, and self-efficacy levels. The study was conducted with 14 high school students attending Uskudar Municipality Youth Academy between 2018 and 2019. In the study, the Perceived Stress Scale (PSS), the Mindfulness Attention Awareness Scale (MAAS), and the General Self-Efficacy Scale (GSES) were used. The experimental group (n = 7) received a 6-session psychoeducation group program (MP), while the control group (n = 7) received no psychoeducation. A two-way (two-factor) repeated-measures ANOVA was performed for data analysis. The findings revealed that the MP was significantly effective in reducing high school students' perceived stress levels and increasing their mindfulness and self-efficacy levels. The findings of the study were reviewed in light of the literature, allowing for certain recommendations to be put forth for counselors and researchers in the field.