Objective: Mindful walking (MW) intervention could be an effective strategy to address the psychosocial stressors and physical health challenges faced by COVID-19 long haulers. This study aims to test the feasibility of digitally delivering MW intervention among long haulers via social media and assess its preliminary efficacy in enhancing physical and psychosocial well-being. Method: We recruited 23 participants via Facebook groups in March and November 2021 for a 4-week online MW intervention, consisting of mindfulness practices (2 sessions per week), delivered entirely through the Facebook group. The intervention was assessed using mixed methods. Quantitative data were collected through 28-day brief daily evening surveys over the 4-week intervention period, including affect, cognition, mindfulness, physical activity, and MW engagement. Qualitative data were extracted from Paradata (i.e., participants responses to the social media posts). Multilevel modeling was employed for statistical analysis and a pragmatic approach was used for qualitative analysis. Results: The mean feasibility score was 4.93/7 (SD=1.88). Multilevel models showed that MW uptake on a given day was positively associated with positive affect (beta=0.89, p<0.01), perceived cognition (beta=0.52, p<0.05), and physical activity levels (beta=0.41, p<0.05), and negatively associated with negative affect (beta=-0.83, p<0.01). The total number of MW days across the study period was positively associated with mindfulness levels (beta=0.3 p<0.01). Paradata reported satisfaction in mindfulness skill enhancement, symptom management, and well-being promotion. Conclusion: The digital delivery of our MW intervention via Facebook showed high acceptability. Preliminary efficacy findings indicate improved mental well-being and physical activity among long haulers.