The effect of intensive voice therapy (Lee Silverman Voice Treatment, LSVT) on vocal tremor features of Parkinson speakers is presented. Vocal tremor is the low-frequency variation of the vocal frequency. Its features differ for Parkinson and normophonic speakers. Here, vocal tremor features have been estimated for a corpus of speakers with Parkinson's disease, recorded before and after intensive voice therapy. Results show that the treatment has significant effects on vocal tremor amplitude: Vocal tremor amplitude has decreased right after treatment. After six month, it has increased again, but is still lower than before treatment.