Objective The aim of this study was to investigate the relations between fragmented QRS complex (fQRS) on ECG and the incidence of ventricular arrhythmias in patients with a prior myocardial infarction (MI). Methods A total of 321 patients with MI were divided into the fQRS (n = 167) and non-fQRS group (n = 154). Standard 12-lead ECG and 24-h Holter monitoring were performed in all patients. Results The incidence of frequent (28.7% vs 17.5%, P< 0.05) or high-risk ventricular premature contractions (34.1% vs 23.4%, P< 0.05) in the fQRS group was higher than in the non-fQRS group. The incidence of non-sustained ventricular tachycardia in the fQRS group was also higher than in the nonfQRS group (12.0% vs 4.5%, P< 0.05). Patients with a fQRS duration of > 0.12 s had a higher incidence of ventricular arrhythmias (70.6%) than patients with fQRS duration between 0.101 and 0.119 s (42.6%, P< 0.05), or those with fQRS duration of 0.10 s or less (22.9%, P< 0.05). Logistic regression analysis showed that fQRS was an independent predictor for high-risk ventricular premature contractions (OR, 1.482, 95% CI, 1.19-3.22, P= 0.02), or non-sustained ventricular tachycardia (OR, 1.982, 95% CI, 1.30-3.76, P= 0.01). Conclusion fQRS was associated with an increased incidence of high-risk ventricular premature contractions and non-sustained ventricular tachycardia. fQRS may be used to predict future risk of ventricular arrhythmias in patients with a prior myocardial infarction.