Objective: To test the effects of Life Enhancing Activities for Family Caregivers (LEAF), a 6-week positive emotion regulation intervention, on outcomes of positive emotion, depression, anxiety, and physical health as measured by the Patient-Reported Outcomes Measurement Information System® (PROMIS®). Method: A randomized controlled trial (N 170) comparing LEAF (N 86) to an emotion reporting/waitlist condition (N 84) in dementia caregivers. LEAF was individually delivered online by trained facilitators. Participants in the control condition completed daily online emotion reports and then crossed over into the intervention condition after 6 weeks. The study was registered with Clinicaltrials. gov (NCT01825681) and funded by R01NR014435. Results: Analyses of difference in change from baseline to 6 weeks demonstrated significantly greater decreases in PROMIS® depression (d <.25; p.02) and Quality of Life in Neurological Disorders (NeuroQOL) anxiety (d <.33; p-.01), as well as improvements in PROMIS® physical health (d.24; p.02) in the intervention condition compared to the emotion reporting/waitlist control. The intervention also showed greater improvements in positive emotion (d.58; p-.01) and positive aspects of caregiving (d.36; p-.01). Increases in positive emotion significantly mediated the effect of LEAF on depression over time. Conclusions: This randomized controlled trial of the online-facilitated positive emotion regulation intervention in dementia caregivers demonstrated small to medium effect sizes on caregiver well-being and shows promise for remotely delivered programs to improve psychological well-being in caregivers of people with dementia and other chronic illnesses.