OBJECTIVE: Mindfulness-based interventions (MBIs) targeting cancer-related emotions and quality of life have attracted extensive attention in recent years. The purpose of the current study was to assess the feasibility and acceptability of an online mindfulness-based intervention and examine its effects on Chinese breast cancer survivors. METHODS: Sixty-five breast cancer survivors were randomized to either an online MBI or to wait for the next available program. The control group received usual care, while the intervention group also received six weeks of online MBI training. Participants completed the Short Form of the Fear of Cancer Recurrence Inventory (FCRI-SF), Five Facet Mindfulness Questionnaire (FFMQ) and European Organization for Research and Treatment of Cancer questionnaire (EORTC-QLQ-C30) at baseline (T1), immediately after the intervention (postintervention: T2) and 1 month later (1-month postintervention: T3). In addition, answers provided to questions about the experience of participating in the course were analyzed. RESULTS: Compared with the control group, the mindfulness, emotional and cognitive function of the MBI group was significantly improved after the intervention, and the FCR of breast cancer survivors was significantly alleviated. These effects were still significant 1 month after the end of the intervention. Additionally, participants were satisfied with the online MBI through the qualitative survey. CONCLUSION: This online MBI showed promise for Chinese breast cancer survivors, facilitating a reduction in FCR and improving their quality of life. The results of our study indicated that online MBI treatment could offer a scalable approach to manage FCR and maintain mental health for breast cancer survivors.