The study is to investigate the role, the duties and efficacy of teaching assistants based on instructors' opinions from eighteen technological and vocational colleges in central Taiwan and further made suggestions for training strategies to improve efficacy. This research adopts Interview and questionnaires, 450 questionnaires distributed and 307 returned. The result shows that teachers think TAs should focus on experimental operation. Moreover, there is no difference between teachers' viewpoints from public and private schools. As for evaluation criteria, TAs should understand related regulations. In terms of training strategy, those with excellent professional grades are prioritized to be teaching assistants.