PURPOSE: Cancer is the second leading cause of mortality worldwide. Cancer negatively affects individuals' quality of life and overall health. Mindfulness-based interventions appear to be promising in the reduction of cancer- and treatment-related symptoms. This review aimed to determine the effectiveness of online mindfulness-based interventions on distress, anxiety, depression, stress, mindfulness, sleep disturbance, quality of life, rumination, fear of cancer recurrence, fatigue and post-traumatic growth among adult cancer patients. METHODS: A literature search was conducted across five electronic databases. Only randomized controlled trials were eligible. Two reviewers independently screened the studies, extracted data, and performed quality assessment using the Cochrane risk of bias assessment tool. Meta-analyses were conducted using review manager software, and standardized mean difference was used to determine intervention effects. Heterogeneity was examined using the I2 statistics. RESULTS: Ten studies were included with a total of 962 participants. Analyses revealed that online mindfulness-based interventions was effective in reducing distress (I2 = 98%；standardized mean difference = -2.21，95% confidence interval: -3.84 to 0.57；P = 0.008)， depression (I2 = 45%；standardized mean difference = -0.33，95% confidence interval: -0.64 to -0.03；P = 0.03), stress (I2 = 97%；standardized mean difference = -2.14，95% confidence interval: -4.24 to -0.03；P = 0.05) and sleep disturbance (I2 = 54%；standardized mean difference = -0.30，95% confidence interval: -0.59 to -0.01；P = 0.04), and improving quality of life (I2 = 94%；standardized mean difference = 0.92，95% confidence interval: 0.09-1.76；P = 0.03). The online mindfulness-based interventions had no significant effects on anxiety, mindfulness, rumination, fear of cancer recurrence, fatigue and post-traumatic growth. Subgroup analyses revealed that online mindfulness-based interventions resulted in higher effect sizes for distress when delivered by website than application, significantly higher effect sizes were also found for online mindfulness-based interventions with guidance, but not on treatment or cancer type. For sleep disturbance, and quality of life, no significant differences between subgroups were found. CONCLUSION: These results provide preliminary support that online mindfulness-based interventions may be feasible and acceptable, which can be used as an adjuvant therapy for the management of cancer-related symptoms among cancer patients.