PURPOSE: this study aims to analyze the objective and subjective evaluation of voice quality in a unilateral vocal fold mobility alteration on prior and post speech therapy. METHODS: this is a retrospective study through chart review, which analyzed the recorded voices of 12 individuals with otorhinolaringology diagnosis of unilateral vocal fold paralysis. The collected material was the sustained emission of the vowel /a/, and then connected speech. The voices before and after therapy were analyzed by using GRBASI scale. The parameters for spectrographic analysis were: shape of the spectrographic tracing, degree of browning of harmonics, stability of the tracing of harmonics, presence of noise, presence of harmonics, presence of sub-harmonics and harmonics definition. The measurement of the maximum phonation time for the vowel /a/ represented the highest value among three emissions. The obtained data were submitted to statistical analysis through Wilcoxon Test Ranking. RESULTS: in the perceptual analysis, the parameter that has changed in the post-treatment was breathiness (B) (p=0.003), followed by dysphonia grade (G) (p=0.004) and asthenia (A) (p=0,01), and those results were statistically significant. As for the spectrogram, we found an improvement of the tracing in 91% of patients, and the changed parameters were: increase in number of harmonics (32%) and reduction in noise (24%). Measurement of the maximum phonation time of the vowel /a/ was higher in the post-speech therapy (p = 0.003). CONCLUSION: speech therapy treatment of unilateral vocal fold paralysis improved perceptual-hearing and spectrographic data and the maximum phonation time of voice.