IMPORTANCE: Quality of life (QOL) of patients with atopic dermatitis (AD) is reported to be the lowest among skin diseases. To our knowledge, mindfulness and self-compassion training has not been evaluated for adults with AD. OBJECTIVE: To evaluate the efficacy of mindfulness and self-compassion training in improving the QOL for adults with AD. DESIGN, SETTING, AND PARTICIPANTS: This randomized clinical trial conducted from March 2019 through October 2022 included adults with AD whose Dermatology Life Quality Index (DLQI) score, a skin disease-specific QOL measure, was greater than 6 (corresponding to moderate or greater impairment). Participants were recruited from multiple outpatient institutes in Japan and through the study's social media outlets and website. INTERVENTIONS: Participants were randomized 1:1 to receive eight 90-minute weekly group sessions of online mindfulness and self-compassion training or to a waiting list. Both groups were allowed to receive any dermatologic treatment except dupilumab. MAIN OUTCOMES AND MEASURES: The primary outcome was the change in the DLQI score from baseline to week 13. Secondary outcomes included eczema severity, itch- and scratching-related visual analog scales, self-compassion and all of its subscales, mindfulness, psychological symptoms, and participants' adherence to dermatologist-advised treatments. RESULTS: The study randomized 107 adults to the intervention group (n = 56) or the waiting list (n = 51). The overall participant mean (SD) age was 36.3 (10.5) years, 85 (79.4%) were women, and the mean (SD) AD duration was 26.6 (11.7) years. Among participants from the intervention group, 55 (98.2%) attended 6 or more of the 8 sessions, and 105 of all participants (98.1%) completed the assessment at 13 weeks. The intervention group demonstrated greater improvement in the DLQI score at 13 weeks (between-group difference estimate, -6.34; 95% CI, -8.27 to -4.41; P < .001). The standardized effect size (Cohen d) at 13 weeks was -1.06 (95% CI, -1.39 to -0.74). All secondary outcomes showed greater improvements in the intervention group than in the waiting list group. CONCLUSIONS AND RELEVANCE: In this randomized clinical trial of adults with AD, integrated online mindfulness and self-compassion training in addition to usual care resulted in greater improvement in skin disease-specific QOL and other patient-reported outcomes, including eczema severity. These findings suggest that mindfulness and self-compassion training is an effective treatment option for adults with AD. TRIAL REGISTRATION: https://umin.ac.jp/ctr Identifier: UMIN000036277.