Literatures indicated the respirators are required and in use in only 20-30% of the work phases [4]. It is postulated that work wearing respirator at constant load under prolonged condition may cause additional physiological strain due to restriction of heat loss from the respiratory system [1,3] and the anaerobic respiration. This study aimed to evaluate the effects of wearing respirators at constant work load under prolonged conditions. Eight male and eight female physically fit university students [3] voluntarily participated in the study, which was approved by the IRB of CMU. A full-face respirator and a control quarter-face mask were employed. The evaluated independent variables included gender, work time (10 and 50 min) and respirator type. Besides, for the prolonged exercise condition, the data during initial 10 minute (D1) and last 10 minute (D5) were also analyzed. The evaluated dependent variables were summarized. Subjective rate of perceptual exertion (RPE) were measured with a 10 point Borg scale questionnaire. All subjects carried out the basic aerobic data measurement and 4 experiments at 3 different days with at least one day off between the experiment days. On the first day the maximal oxygen consumptions were measured using a revised protocol [2]. The total 4 experiment conditions were completely randomized. The physiological variables were analyzed by repeated measure ANOVAs . The subjective RPE was analyzed using Wilcoxon test. The ANOVAs and some descriptive statistics are summarized. Results indicated that working for constant load under prolonged condition significantly increased minute ventilation (p<0.001), oxygen consumption (p<0.001), working pulse (p<0.05),metabolic rate (p<0.001) and total RPE (p<0.001). While comparing the D1 with D5, the similar trends were found more significantly especially for female subjects. The oxygen consumption were found significantly increased from 1.09±0.04 (D1) to 1.86±0.04 liter/min (D5). It is suggested that the work-rest ratio should be reconsidered under constant load prolonged work and micro break may be helpful which need further study.