BACKGROUND: Social anxiety is increasingly prevalent among youths, leading to social withdrawal, isolation, and heightened depression risk. Mobile health (mHealth) interventions offer anonymity, accessibility, and personalized support, but their effectiveness and cost-effectiveness for young individuals with social anxiety remain unclear. OBJECTIVE: This randomized controlled trial aims to evaluate the effectiveness and cost-effectiveness of a mobile-based psychoeducation program (OkeyMind) for mitigating social anxiety symptoms among youth. METHODS: Participants aged 15 years through 24 years with mild or more severe social phobia (Social Phobia Inventory [SPIN] ≥25) and access to WeChat will be recruited and screened onsite and then randomly assigned to the intervention or waiting list control group. The study will recruit 180 participants, with 90 in each group. The intervention group will receive a 1-month mobile psychoeducation program (OkeyMind), which includes both psychoeducation and meditation components, with all content fully automated. The waiting list control group will receive the same intervention after 3 months. The primary outcome is social anxiety symptoms measured using SPIN. Secondary outcomes include depression (Patient Health Questionnaire-9) and health-related quality of life (EuroQol-5). Assessments will be conducted at baseline, postintervention, and a 3-month follow-up. RESULTS: Recruitment began in September 2024. The study was funded in April 2024, and the first participant was enrolled in September 2024; as of the end of March 2025, 132 participants had been recruited. Recruitment is ongoing. Data collection will conclude in July 2025, after which data analysis will begin and be completed in August 2025, with primary findings targeted for publication in spring 2026. CONCLUSIONS: This research evaluates the effectiveness and cost-effectiveness of OkeyMind, a mobile-based psychoeducation program, for reducing social anxiety symptoms among youth. OkeyMind might be a promising strategy for combating social anxiety, especially in low- and middle-income countries with limited medical resources. If effective, this intervention could provide an accessible, cost-effective approach to managing social anxiety, particularly in resource-limited settings. TRIAL REGISTRATION: ClinicalTrials.gov NCT06490315; https://clinicaltrials.gov/study/NCT06490315. INTERNATIONAL REGISTERED REPORT IDENTIFIER (IRRID): PRR1-10.2196/64518.