This was a secondary analysis of a pilot randomized controlled trial (RCT) of mindfulness-based stress reduction (MBSR) among young adult (YA) survivors of cancer, which showed preliminary evidence for improving psychosocial outcomes. Secondary outcomes assessed were the feasibility of collecting biological data from YAs and preliminary effects of MBSR on markers of inflammation and cardiovascular function. Participants were randomized to 8-week MBSR or a waitlist control condition. Participants provided whole blood spot samples for analysis of C-reactive protein (CRP) and interleukin (IL)-6 as well as blood pressure data in-person at baseline and 16-week follow-up. Feasibility was assessed with rates of providing biological data. Linear mixed effects modeling was used to evaluate preliminary effects of MBSR on inflammatory markers and blood pressure over time. Of 126 total participants enrolled, 77% provided biological data at baseline (n = 48/67 MBSR, n = 49/59 control). At 16weeks, 97% of the 76 retained participants provided follow-up biological data (n = 34/35 MBSR, n = 40/41 control). Relative to the control group, MBSR was associated with decreased systolic blood pressure (p = 0.042, effect sizes (ES) = 0.45) and decreased diastolic blood pressure (p = 0.017, ES = 0.64). There were no changes in CRP or IL-6. This was the first study to explore the feasibility of collecting biological data from YA survivors of cancer and assess preliminary effects of MBSR on inflammatory and cardiovascular markers in an RCT. Minimally invasive biological data collection methods were feasible. Results provide preliminary evidence for the role of MBSR in improving cardiovascular outcomes in this population, and results should be replicated.