Diplophonia is produced by the voice of two separate tones and produced through quasi-periodic variations in the vocal cord vibration. Diplophonia is generally regarded as a symptom of laryngeal pathology. The difference in the vibratory frequency between the vocal cords can be seen in a tension imbalance and a difference in the level of the vocal folds under special conditions such as incomplete glottal closure. So we can easily find diplophonia in the patient of unilateral vocal cord paralysis(superior and/or inferior). But there are some cases of diplophonia in patients with mass lesion of the vocal fold, intracordal cyst and others. The authors have experienced 19 cases of patient with diplophonia secondary to unilateral vocal cord paralysis, intracordal systs and other mass lesion. We analysed the diplophonic voice with perceptual evaluation, number of vibratory cycles, peak variability and noise level for the quasi-periodic waveforms before and after surgery. On the acoustic data before surgery, there were no significant differences between the unilateral vocal fold paralysis and the lesions with mass imbalance. But on the acoustic data for the diplophonic voice with unilateral vocal fold paralysis after surgery, there was marked improvement of acoustic data compared with the data before surgery.