This paper derived four acoustic parameters reflecting voice quality improvement by voice training. Voice training corrects respiration, phonation, articulation, and facial expression. The purpose of this study is to develop acoustic parameters which quantitatively represent the quality of each training item. This paper examined six acoustical feature parameters on the performance as the measure for voice quality improvement. Experimental results indicated that four of the six parameters, the intensity of harmonic structure, the dynamic range of the spectral envelope, formant intensity, and spectral slope were significantly improved after the training. Further analyses were carried out on the correlation between subjective evaluation and above acoustic properties. The results indicated that abdominal respiration was most important for improving these four parameters.