A Chinese aspiration is generally considered to be very difficult for Japanese students to reproduce. We measured the voice on set time (VOT) and mean breathing power during VOT, as evaluation parameters, of diphthong sounds of the labial of pai[p'ai], pao[p'ao], pei[p'ei], and pie[p'iε] and diphthong sounds of the alveolar of tai[t'ai], tao[t'ao], tie[t'iε], and tou[t'ou] in Chinese aspirations uttered by nine Japanese students and nine native Chinese speakers. The sounds were evaluated by the listening test of eight native Chinese speakers. We found that the VOT was not the sole measure for evaluating the pronunciations; the mean breathing power during VOT is also a useful measure for evaluation. Keywords: Chinese Aspiration, Pronunciation, VOT, Breathing Power