Objectives <p>Based on the literature linking mindfulness with decentering and with better interactions with others, this study aimed to examine the associations of daily mindfulness and decentering with the mother–child relationship and with mothers’ well-being, during the first COVID-19 lockdown.</p> Method <p>The study involved 84 mothers with an average age of 40.25&#xa0;years (<i>SD</i> = 6.75), who completed daily online questionnaires, and were randomly assigned to one of two interventions: mindfulness practice or listening to relaxing music (active control group).</p> Results <p>The findings indicated a significant association between mothers’ daily mindfulness levels and their relationships with their children on the same day, including increased frequency of hugs and improved daily communication with children. Additionally, a significant association was found between daily mindfulness and decentering, and daily decentering was also associated with mother–child relationships, including improvements in communication quality and increased frequency of hugs. Decentering was also associated with mothers' well-being, reflected in increased positive emotions and decreased negative emotions. However, no differences were found between the intervention groups.</p> Conclusions <p>This daily diary study highlights the associations of mindfulness and decentering with daily aspects of mother–child relationships and mothers’ well-being during crisis. The study emphasizes the potential of further research to explore how mindfulness influences relationships and other aspects of daily life, to advance the understanding and application of mindfulness and mindfulness practice as a means of psychological support.</p> Preregistration <p>This study was not preregistered.</p>