The purpose of this research is to investigate the effect of 9 week simulated hypoxic training using gas mask on cardiopulmonary function and performance of 8 middle and long distance endurance athletes. After the training period the following changes were observed. Experimental and control group improved in treadmill exercise time 8.4% (p<.05) and 15.8% (p<.01) respectively. In performance test experimental group increased their running speed in 1,500m, 5,000m, and 10,000m. Meanwhile, control group increased their running speed in 5,000m and 10,000m. In blood composition alteration following the training experimental group showed 4.2%(p<.05) increase in exercise recovery Hct. Control group showed 2.5%(p<.02) and 3.8%(p<.01) increase in exercise recovery Hgb and Hct. In aerobic capacity experimental group showed 5.65 and 7.7% (p<.05) imrovement in VO₂max(ml/kg/min) and MV. Both groups demonstrated little change in anaerobic capacity represented by anaerobic threshold(=AT). In OBLA experimental group showed 8.9%(p<.05) and 23.7% increase in OBLA-% VO₂max and OBLA-MV. In conclusion experimental group did not demonstrate the significant training effects in all variables. However, We found, in some variables, the positive answers concerning the hypoxic training effects. It is believed that both groups already reached high level of cardiopulmonary function and performance before they start training and that might affect the results of this experiment.