Background <p>Although working women experience significant work-related stress, preventive interventions to reduce its negative impact on their mental health are inadequate. Interventions for improving sleep quality have been effective in reducing the negative effects of work-related stressors. Mindfulness-based interventions have been effective in improving sleep quality. We evaluated the effectiveness of an eight-week mindfulness meditation intervention, provided via a smartphone application, on working women’s subjective sleep quality and daily physiological indicators through a randomized controlled trial. This study recruited working women by opportunity sampling, social media, and a website. Participants were randomly assigned to either the intervention (<i>n</i> = 25) or waitlist control group (<i>n</i> = 28). Those in the intervention group practiced app-based mindfulness meditation every day for as many days as possible for eight weeks. Conversely, participants in the waitlist control group continued as usual for eight weeks. Subsequently, they began practicing mindfulness meditation every day after eight weeks. Participants wore a wearable device during the experimental period. We assessed their subjective sleep quality (Insomnia Severity Index [ISI]) pre- and post-intervention and physiological indicators, which were assessed via the wearable device. We examined the intervention × time point interaction effect for ISI scores and the intervention × day effects for physiological indicators.</p> Results <p>We analyzed 75 data points (intervention condition, <i>n</i> = 49; control condition, <i>n</i> = 26) in the condition comparison analysis. The interaction effect was significant for daily resting heart rate (γ= -0.08, <i>p</i> &lt; .001) and marginally significant for ISI scores (<i>b</i> =-2.04, <i>p</i> = .051) and the rate of non-rapid eye movement (REM) sleep (γ = 0.00, <i>p</i> = .06). Participants in the intervention condition demonstrated a significant decrease in ISI scores (<i>b</i> =-1.55, <i>p</i> = .013) and a marginally significant decrease in heart rate during non-REM sleep (γ=-0.04, <i>p</i> = .07).</p> Conclusions <p>These findings indicate that app-based mindfulness meditation was effective in improving subjective and objective sleep quality among working women. Therefore, app-based meditation is a promising intervention.</p> Trial registration <p>Japan Registry of Clinical Trials (JRCT) jRCT1030240315 (registration date: 2 September 2023); <a href="https://jrct.mhlw.go.jp/en-latest-detail/jRCT1030240315">https://jrct.mhlw.go.jp/en-latest-detail/jRCT1030240315</a>.</p>