Spastic dysarthria is a motor speech disorder produced by a damage to the direct (pyramidal) and indirect (extrapyramidal) pathways of the central nervous system. This study attempted to determine the influences of the severity of spastic dysarthria on the stability of voice. A sustained /a/, /a/ produced at the beginning of a sentence and at the end of the sentence were analyzed. The Praat 4.0.51 was used for analysis. The results showed a significant difference between the severe spastic dysarthric group and normal group matched by age and sex at the beginning and the end of the sentence. In addition, the severe group showed a significant difference between the first /a/ and the second /a/ at the end of sentence.