Background Maximal oxygen uptake (VO 2 max) is a useful index to assess exercise capacity. However, there is no reference value for Koreans. This study aimed to compare actual VO 2 max and predicted VO 2 max using exercise capacity equations in Korean subjects. Methods This retrospective study enrolled 383 patients who underwent cardiopulmonary exercise test (CPET) with incremental maximal cycle ergometer test at Asan Medical Center from January 2020 to May 2021. Stage 1 and 2 lung cancer patients with normal lung function and healthy persons of 50 subjects who had maximal CPET were analyzed. Results The subjects were aged 65 ± 13 years and predominantly male (74%). CPET results were as follows: absolute VO 2 max, 1.2 ± 0.3 L/min; body weight referenced VO 2 max, 20 ± 3.9 mL/kg/min; peak work rate, 94 ± 24 watts; peak heart rate, 142 ± 21 bpm; peak O 2 pulse, 10 ± 3 mL/beat; minute ventilation, 59 ± 14 L/min; peak respiratory rate, 34 ± 6 breaths per minute; and peak breathing reserve, 41 ± 18%. There was significant discordance between the measured and predicted absolute VO 2 max using the Jones, Hansen, and Wasserman prediction equations developed for Caucasian population ( P < 0.001). Agreement using Bland-Altman test between true and predicted absolute VO 2 max was the best in Chinese equation (−0.03, 2SD = 0.55) compared to Jones (0.42, 2SD = 1.07), Hansen (0.44, 2SD = 0.86), and Wasserman (0.42, 2SD = 0.86) equations. Conclusion The reference value and prediction equation from studies including primarily Caucasians may not be appropriate for Koreans. Since the mean difference is the lowest in Chinese equation, the Chinese equation might be used for the Korean adult population.