Objectives : The object of this study was to evaluate repeatability of portable spirometry and to determine an appropriate equation for predicted value. Materials and Methods : The subjects were 76 men and 45 women recruited from among Kyunghee University oriental medical students. Portable spirometry was performed via the procedure recommended in ATS guidelines. Repeatability of spirometry was checked against ATS repeatability standards and NHLEP QC grade. Percentage of predicted value of non-smokers was calculated through a Caucasian population-based regression equation(by Morris et al.) and Korean population based regression equation(by Kim et al.). These were compared. Result : 91.7% of subjects matched repeatability standards of ATS and 95% of subjects got interpretable NHLEP QC grades of A, B, and C. Mean percentage of predicted value by Morris et al. were as follows: Mean of FVC% was 90.86, FEV1% was 96.66, FEV1/FVC% was 107.48. Mean percentage of predicted value by Kim et al. were as follows. Mean FVC% was 92.38, FEV1% was 89.77, FEV1/FVC% was 96.95. Conclusions : Results of this study show that more than 90% of subjects meet repeatability criteria. This supports a role for the portable spirometer as a primary oriental medical office tool. Further, results are a verify that they Korean population-based predicted value equation is a more appropriate standard than the Caucasian population-based one, but a still more accurate standard is needed for the Korean adult population.