To investigate the association between cognitive function and postoperative stroke in patients undergoing off-pump coronary artery bypass grafting (CABG). We reviewed patients who underwent cognitive evaluations including Montreal Cognitive Assessment (MoCA), Mini-Mental State Examination (MMSE), Pittsburgh Sleep Quality Index (PSQI), and Activities of Daily Living (ADL) scale before CABG. The association between cognitive function and postoperative stroke was analyzed. A total of 1,932 patients were analyzed. Postoperatively, 34 (1.8%) developed new-onset stroke.Poststroke patients showed lower MMSE (27.0 [23.2-28.0] vs. 28.0 [27.0-29.0], p < 0.001) and MoCA scores (21.0 [18.0-23.8] vs. 24.0 [21.0-27.0], p < 0.001), but similar PSQI and ADL scores compared to those without stroke. After stepwise regression, preoperative stroke (OR = 7.07, p < 0.001) and MoCA scores (OR = 0.90 / point, p = 0.002) were predictors of postoperative stroke. Preoperative cognitive function evaluated by MoCA is associated with postoperative stroke following CABG.