Mindfulness‐based stress reduction (MBSR) is an effective program for improving well‐being. A growing body of studies is exploring the mechanisms mediating its beneficial effects. Integrative self‐knowledge (ISK) is the construct of focus in this study. The primary goal of the current study was to investigate the mediating role of ISK in the relationship between improved mindful observing (MO), non‐judging inner experience (NJ), and well‐being following an MBSR program with an Iranian sample. Participants (n = 118) enrolled in MBSR and completed depression, anxiety, stress (DASS), Bartone Symptoms Checklist (BSC), Five‐Facet Mindfulness Questionnaire, and ISK scale before and after the program. Results showed significant reductions in BSC, DASS, and improvements in MO, NJ, and ISK at the end of the program. Mediation analyses revealed that changes in ISK significantly mediated the relationship between changes in MO and NJ and symptoms (MO indirect effect on DASS: β = 0.11, confidence interval [CI] [0.003, 0.29]; NJ indirect effect on DASS: β = 0.12, CI [−0.16, 0.45]; MO indirect effect on BSC: β = 0.08, CI [0.001, 0.27]; NJ indirect effect on BSC: β = 0.09, CI [0.01, 0.22]). Improvements in MO and NJ may provide a pathway to cultivating ISK in MBSR, which may lead to enhanced well‐being. [ABSTRACT FROM AUTHOR]