Background: Fragmented QRS (f-QRS) complexes are novel electrocardiographic signals, which reflect myocardial conduction delays in patients with coronary artery disease (CAD). The significance of f-QRS complexes in non-ST elevation ACS patients for detection of the severity of CAD (correlation with Syntax score) was evaluated in this prospective study. Methods: A total of 104 patients with non-ST-elevation ACS who underwent invasive coronary angiography for detection of coronary artery disease were recruited prospectively in this study, ECG was done to all patients, which showed f-QRS in 50 patients (f-QRS group) and inverted T wave or depressed ST in 54 patients (non f-QRS group). The significance of f-QRS complexes on 12-lead ECG for detection of the severity of the CAD (correlated with Syntax score) was assessed in this cohort of patients. Results: Among the patients studied, elderly patients (age ⩾ 65 years), males, diabetics, smokers and those with dyslipidemia had a significantly higher frequency of fQRS complexes (with P value = 0.02, 0.01, 0.019, 0.005, 0.02 respectively). Also, the present study found a higher frequency of f-QRS in patients with multi-vessel disease, in those with more severe degree of coronary artery stenosis, in those with positive Troponin I level and in those with high Syntax score (with P value = 0.009, 0.000, 0.000 respectively). Conclusions: The frequency of f-QRS complexes was found to be higher in elderly, diabetic, dyslipidemic, and male patients with NSTE-ACS. The higher frequency of (f-QRS) was correlated with the extent and severity of coronary lesions in patients with NSTE-ACS.