Objectives: This systematic review and meta-analysis examined the effects of mindfulness-based interventions (MBIs) on psychological symptoms, cognitive functions, and quality of life in older adults with dementia or mild cognitive impairment (MCI). Methods: A comprehensive search was conducted within four databases to identify relevant randomized controlled trials (RCTs). Heterogeneity was assessed using the I2 statistic. Depending on I2 statistic values, either a random effects model or fixed effects model was used. Results: 10 RCTs published in 11 articles met the eligibility criteria. The present meta-analysis study found no significant effect of MBIs on depressive symptoms, anxiety, quality of life, memory, and overall cognitive functions compared to control groups. Conclusions: Future high-quality studies involving different types of MBIs are needed to better understand the effects of MBIs on psychological symptoms, quality of life, and cognitive functions in older adults with MCI and dementia and examine effective intervention features. Clinical Implications: There is insufficient evidence to determine whether or not practitioners should be routinely providing MBIs to older adults with MCI and dementia due to the lack of studies currently.