This study investigated how task-based learning (TBL) developed the verbal competence of Chinese learners of English as a foreign language (EFL) by employing qualitative and quantitative analyses. We compared the impromptu oral presentations on reading texts of 76 intermediate EFL learners given respectively in the beginning and the end of the 15-week study period at a Taiwanese university. The findings revealed that TBL was effective in fluency, lexical and syntactic complexity, and ineffective in accuracy. Besides, a standardized pretest and a post-test of English proficiency were administered, apart from a students' self-report questionnaire at the end of the experiment. The results of the proficiency exams showed that students made significant improvements in reading and little improvement in listening after TBL. In the self-assessment of the effects of TBL, students felt improvements in vocabulary and pronunciation. Overall, TBL was motivational and useful for language acquisition. Learners' attention was directed to a reading text as a whole for communicative purposes, and therefore their receptive and productive competence was enhanced.