OBJECTIVE: To test whether Mindfulness-Based Cognitive Therapy to Prevent Suicide (MBCT-S) is associated with improvement in attentional control, an objective marker of suicide attempt. METHOD: In the context of a randomized clinical trial targeting suicide risk in Veterans, computerized Stroop and emotion Stroop (E-Stroop) tasks were administered 3 times over 6-months follow-up to 135 high suicide risk Veterans. Seventy were randomized to receive MBCT-S in addition to enhanced treatment as usual (eTAU), and 65 were randomized to eTAU only. E-Stroop word types included positively- and negatively-valenced emotion, suicide, and combat-related words. Interference scores and mixed effects linear regression analyses were used. RESULTS: Veterans receiving MBCT-S showed a more favorable trajectory of attentional control over time, as indicated by performance on two E-Stroop tasks. Combat-stress interference scores improved over time among Veterans in MBCT-S. Interference processing time for negative affective words deteriorated over time among Veterans receiving eTAU only. CONCLUSIONS: MBCT-S may effectively target attentional control, and in particular reduce processing time during affective interference, in high suicide risk Veterans. Future studies to replicate these findings are warranted.