Signal-averaged electrocardiography (SAECG) has been known to be useful for prediction of lethal ventricular arrhythmias (VA). However, this technique has limitations in patients with intraventricular conduction disturbance (IVCD), which is common in cardiac sarcoidosis (CS). Meanwhile, wavelet-transformed ECG (WTECG) has been reported to be useful for detecting arrhythmogenic substrate hidden within QRS complex. The objective of this study was to assess the utility of WTECG for detecting arrhythmogenic substrate in patients with CS. Forty-four CS patients including 18 patients with VA were retrospectively investigated. The parameters on the signal-averaged electrocardiography (SAECG) and the power of frequency components on WTECG were compared between VA group and non-VA group. Eighteen patients have VA (VT: n = 17, VF: n = 1). LP were detected in 17 in VA group and 24 in non-VA group. WTECG showed that high-frequency components (HFC; 80–150 Hz) were developed in VA group. Peak power value at 150 Hz (P150) was significantly higher in VA group than that in non-VA group (442.9 ± 160.2 vs 316.7 ± 100.8, p = 0.006). The receiver operating characteristic (ROC) curve analysis showed an optimal cutoff point of 336 of P150 for detecting patients with VA, with 82.4% sensitivity, 61.5% specificity, and area under the curve of 0.74 (95% confidence interval [CI] 0.59–0.89). WTECG may be useful for detecting CS patients who are prone to VA.