The objective of this study is to investigate the effectiveness of the personal hearing protective devices in terms of the hearing threshold shift and the speech intelligibility index. The hearing threshold shift was used to quantify the protection effect of the personal hearing protective devices and obtained by subtracting the baseline threshold measured without the personal hearing protective devices from the hearing threshold measured with the personal hearing protective devices. The speech intelligibility index (SII) was used to predict and compare the potential benefits of each personal hearing protective device and obtained from the count-the dots method. A total of 6 college students aging from 21 to 25 years old were randomly recruited as subjects. Different types of personal hearing protective devices (earplug and earmuff) were used in this study. A statistically significant difference between the mean amount of threshold shift at low frequency (0.25-1 kHz) and that of high frequency region (2-8 kHz) was observed. The personal hearing protective devices (earplug and earmuff) were effective in protecting hearing from high frequency noises than low frequency noises. The use of earmuff was effective at the low frequency region while the use of earplug was effective at the high frequency region. In addition, the use of the earplug was more effective for the SII than that of the earmuff. The protection amount of the personal hearing protective devices (earplug and earmuff) ranged from 23 to 38 dB. However, the SII ranged from 32.6 to 54.5%, which indicates that the subjects misunderstood or missed the speech information ranged from 45.5 to 67.4% as mild to moderate hearing loss. This may lead to the development of new personal hearing protective devices which are effective for protecting hearing and understanding speech.