Abstract.[Purpose] The aim of this study was to research the physical factors affecting vital capacity (FVC, ERV, MVV) of adults in their 20s.[Methods] Ninety-seven healthy adults without neurological and muscular disorders participated in this study. The physical factors were defined by gender, body mass index (BMI), smoking history, and postures. A Spiropalm (A-M systems, Sequim, WA, USA) was used to measure respiratory function (FVC, ERV, and MVV). Multiple regressions were used to research the physical factors affecting vital capacity (FVC, ERV, and MVV).[Results] The important physical factors found to be significantly associated with FVC, ERV, and MVV were gender and weight (R 2 = 0.756), smoking history (R 2 =0.179), and gender (R 2 =0.427), respectively. [Conclusion] This study indicated that gender and weight are important physical factors for vital capacity in Korean adults in their 20s.