Objective The purpose of this study was to investigate the effects of mindfulness-based stress reduction for breast cancer survivors (MBSR(BC)) on multiple measures of objective and subjective sleep parameters among breast cancer survivors (BCS). Methods Data were collected using a two-armed randomized controlled design among BCS enrolled in either a 6-week MBSR(BC) program or a usual care (UC) group with a 12-week follow-up. The present analysis is a subset of the larger parent trial (ClinicalTrials.gov Identifier: NCT01177124). Seventy-nine BCS participants (mean age 57 years), stages 0-III, were randomly assigned to either the formal (in-class) 6-week MBSR(BC) program or UC. Subjective sleep parameters (SSP) (i.e., sleep diaries and the Pittsburgh Sleep Quality Index (PSQI)) and objective sleep parameters (OSP) (i.e., actigraphy) were measured at baseline, 6 weeks, and 12 weeks after completing the MBSR(BC) or UC program. Results Results showed indications of a positive effect of MBSR(BC) on OSP at 12 weeks on sleep efficiency (78.2% MBSR(BC) group versus 74.6% UC group, p = 0.04), percent of sleep time (81.0% MBSR(BC) group versus 77.4% UC group, p = 0.02), and less number waking bouts (93.5 in MBSR(BC) group versus 118.6 in the UC group, p < 0.01). Small nonsignificant improvements were found in SSP in the MBSR(BC) group from baseline to 6 weeks (PSQI total score, p = 0.09). No significant relationship was observed between minutes of MBSR(BC) practice and SSP or OSP. Conclusions These data suggest that MBSR(BC) may be an efficacious treatment to improve objective and subjective sleep parameters in BCS.