Objective To investigate the effect of the standing position on the amplitudes of QRS waves of 12-lead electrocardiogram (ECG). Methods The ECG was recorded in the supine and standing positions in 60 hospitalized patients or out-patients, and the amplitudes of Q, R, and S waves of all 12 ECG leads were measured and compared between the two positions. Results In inferior leads, the amplitudes of Q waves and R waves in leads Ⅱ, Ⅲ and aVF recorded in standing position were significantly deepened or increased, and S waves in lead Ⅲ recorded in standing position were significantly shallowed compared with those in the supine position(P<0.05). In lateral leads, the amplitudes of Q waves in leads Ⅰ and V5-6, S waves in leads Ⅰ and aVL recorded in the standing positions were significantly shallowed compared with those in the supine positions; R waves in leads Ⅰ and aVL recorded in the standing positions were decreased compared with those in the supine position (P<0.05). In thoracic leads, the amplitudes of R waves in leads V1-4 recorded in the standing position were significantly decreased compared with those in the supine position; the S waves in leads V1-3 waves recorded in the standing position were significantly shallowed compared with that in the supine position(P<0.05); and the R waves of lead aVR recorded in the standing position was significantly increased compared with that in the supine position (P<0.05). Conclusion The amplitudes of QRS waves of ECG are different when recorded in the standing and supine positions.