Energy expenditure during sport activities has been determined traditionally by the Douglas Bag Method and the Motion Time Study. However, those two methods do not yield accurate values when used in long continuous and/or vigorous physical activities. This study, therefore, measured oxygen uptake by means of a portable device “Oxylog”, and determined the energy expenditure of many sport activities. The experiments were carried out with 13 untrained male subjects (UTS), and 30 trained male subjects (TS) . The 30 trained men consited of ten tennis players, ten badminton players and ten basketball players. UTS played one set of doubles (tennis), one set of singles (badminton), two sets of singles (table tennis), two games (bowling) and jogged 10 minutes, But TS played only their major sports : one set of doubles (tennis), one set of singles (badminton) and two 20-minute halves (basketball) . The results were 0.172±0.017kcal⋅kg^-1⋅min^-1 for jogging (UTS), 0.146±0.028kcal⋅kg^-1⋅min^-1 for badminton (TS), 0.133±0.021kcal⋅kg^-1⋅min^-1 for basketball (TS), 0.130±0.018kcal⋅kg^-1⋅min^-1 for badminton (UTS), 0.102±0.016kcal⋅kg^-1⋅min^-1 for tennis (TS), 0.096±0.014kcal⋅kg^-1⋅min^-1 for tennis (UTS), 0.089±0.019kcal⋅kg^-1⋅min^-1 for table tennis (UTS), and 0.055±0.009kcal⋅kg^-1⋅min^-1 for bowling (UTS) . In comparison with UTS, TS exhibited higher values in tennis and badminton. This is considered to result from TS's better training. This result indicates that energy expenditure in playing sports activities depends on the level of player's ability. The method employed in of this study is believed to be the best choice at present. Many other sport activities must be reexamined in detail using this method.