This study explores medical college students' improvement on the TOEIC upon completion of English-only classes by comparing their pre- and post-TOEIC scores. The students' responses on the questionnaire were also reviewed. The subjects were the 44 first-year medical students taking the English-only classes that required active participation of individual presentation, role play and acting in class. Explicit grammar explanation was also given in English and the students were encouraged to use the language exclusively. They were considered intermediate to advanced level as their mean score of the pre-TOEIC score was 702 ranging from 515 to 945. The results of the post-TOEIC showed that 78% of the students (28 out of 36) improved significantly from the mean score 702 to 766 by the average of 64 points. They also responded that the English-only classes help them improve and participate more actively as a form of role play and acting. It was therefore concluded that the English-only classes that comprised student presentation of role play and acting were effective for the intermediate to advanced level medical college students. (Contains 8 tables.)