This paper is to investigate the effectiveness of Prontest software to improve English pronunciation and proficiency for Japanese EFL learners. Several parameters such as speech duration, speech power, F0 (pitch), the ratio of vowel and consonant length and power were introduced to find out how much students made progress in English pronunciation and overall English proficiency. The study concluded that the average score of CASEC computer test improved from 532(SD 109.2) in April to 583(SD 83.1) in July after having used this software for six lessons. The differences of parameters between pre and post-recorded readings indicated that this software helped students to improve English pronunciation.