Acceptance and commitment therapy (ACT) is an emerging evidenced-based practice based on a psychological flexibility model encompassing six processes, including acceptance, cognitive defusion, self-as-context, being present, values, and committed action. ACT aims to improve overall psychological flexibility and the six processes. This systematic review and meta-analysis examined the effects of ACT on measures of purported processes among family caregivers. Four electronic databases were searched from the date of inception of each database to March 30, 2020. A total of 18 studies met the eligibility criteria, including 8 randomized controlled trials (RCTs), 1 nonrandomized control group pretest-posttest design study, and 9 one group pretest-posttest design studies. A meta-analysis of 8 RCTs found a moderate effect of ACT on psychological flexibility among family caregivers at the immediate posttest and follow-up. A meta-analysis of 9 one group pretest-posttest design studies showed a large effect of ACT on psychological flexibility at the immediate posttest and follow-up. No significant effect was found in measures of cognitive fusion, valued living, and mindfulness except for a meta-analysis of 2 RCTs showing a small effect of ACT on cognitive fusion at follow-up. This review discusses synthesized findings, a gap in the literature, and suggestions for future studies.