Korean nail-beauty is mainly concentrated on women in their 20s and 40s. The purpose of this study is to investigate the structure and characteristics of nails based on the literature and to measure the nail size of adult women in their 20s to 40s as an empirical study. The purpose of this study is to utilize the measurement results as basic data for the standardization of nail size through comparative study with previous studies. For the study method, 150 (50 for each age group) adult female in 20 ~ 40 years with cuticle removed for 30 days from September 17 to October 16, 2017 were measured. As the result, As a result of measurements, the width of the nail was almost similar to that of the researcher. However, the thumb was 1.01 mm longer than the results of the previous researchers. The index nail was 1.12 mm longer, the middle nail was 0.82 mm longer, and the ring nail was 1.3 mm longer than the previous study.