Background: Parkinson’ s disease (PD) is a progressive neurological disorder and many PD patients experience some type of Voice and speech disorders during the course of illness. In this study, the aim was to investigate the effect of Lee Silverman Voice treatment (LSVT) on improving Voice difficulties in patients with mild PD using Voice handicap index (VHI). Methods: This interventional study was conducted on 23 PD patients who were randomly divided into 2 groups: a treatment group (PD-T) (n=13) and a no-treatment group (PD-NT) (n=10). Neurologically healthy control (NNC) group consisted of 13 healthy participants who did not suffer from Voice and speech problems and were matched with PD group by age (50-65 years), sex, and education. VHI questionnaire was completed a day before the start of LSVT and a day after the treatment fulfillment for the PD-T group; the same time spots were applied for the PD-NT and NNC groups. Statistical analyses were performed using SPSS Statistics 22. 0 and significance level was set at 0. 05. The multivariate analysis of variance and repeated measure analysis of variance were used for data analysis. Results: PD groups showed a significant weakness in VHI scores before treatment compared to NNC group (p≤ 0. 001). The mean of VHI scores for PD-T, PD-NT, and NNC groups before treatment was 44. 31± 11. 23, 43. 54± 6. 10, and 8. 15± 4. 27, respectively. LSVT was successful in improving VHI scores in PD-T group (17. 23± 5. 35, p≤ 0. 001). However, no improvement was observed in PD-NT group (44. 00± 5. 88). Conclusion: Improvement in VHI score could be the result of ameliorated self-monitoring and self-regulation created by LSVT.