Objective: We intended to compare the standard 12-lead electrocardiogram (ECG) recordings in older patients with bipolar disorder (BD) and schizophrenia (SZ). Methods: We recruited 109 outpatients who were aged over 50 years and had a diagnosis of BD-I or SZ. A board-certified cardiologist who was blinded to clinical information, analyzed the 12-lead ECG recordings. Clinical data were obtained using interview and chart review. Results: We recruited 44 patients with BD and 65 patients with SZ. We found that significantly higher proportion of BD patients had ECG-defined left ventricular hypertrophy than that in SZ patients (13.6% vs. 3.1%, p < 0.05). In addition, patients with BD had significantly higher diastolic blood pressure and body mass index on the day of the most recent psychiatric admission than did those with SZ. Conclusion: Patients with BD are at a greater risk of ECG-defined left ventricular hypertrophy which may link to the unfavorable psychopathological and pathophysiological outcomes of BD itself.