Aim To determine longitudinal changes in functional status using three functional assessment scales in elderly patients undergoing coronary artery bypass grafting. Methods This was a prospective observational cohort study of 73 patients aged ≥60 years undergoing elective coronary artery bypass grafting. Patients were assessed for functional status before admission, at hospital discharge, and at 1 and 6 months after discharge using the Functional Independence Measure, Katz Activities of Daily Living scale, and Lawton Instrumental Activities of Daily Living scale. Data were stratified by age (≥70 years and <70 years) and complications (with and without) for analysis. Results In patients aged ≥70 years (n = 38), Functional Independence Measure scores ranged from 121.30 ± 6.42 (pre‐admission) to 112.10 ± 17.10 (1 month) and 117.80 ± 13.50 (6 months), Katz scores from 5.88 ± 0.32 (pre‐admission) to 5.45 ± 1.04 (1 month) and 5.83 ± 0.65 (6 months), and Lawton scores from 25.40 ± 3.30 (pre‐admission) to 20.05 ± 4.93 (1 month) and 24.50 ± 4.10 (6 months; P < 0.001 for all). No significant changes were found in scale scores over time between groups with (n = 34) and without (n = 39) complications. When groups aged ≥70 years (n = 38) and <70 (n = 35) were compared, Functional Independence Measure scores showed a difference toward recovery over time in older patients (discharge – pre‐admission, P = 0.010; 1 month – pre‐admission, P = 0.0004; and 6 months – pre‐admission, P = 0.079). Conclusions The Functional Independence Measure was able to detect significant functional loss over a 6‐month period in elderly patients undergoing coronary artery bypass grafting, suggesting that this scale is a promising tool for the assessment of functional recovery over time after cardiac surgery, especially in patients aged older than 70 years. Geriatr Gerontol Int 2015; ●●: ●●–●●.