Objectives: This study aims to compare the contents of physical activity questions of Korean National Health and Nutrition Examination Survey(KNHANES), and to propose suggestions for improvement. Methods: Questions measuring physical activity prevalence of adults in the KNHANES from KNHANES I(1998) to the first year of KNHANES V(2010) were compared. Results: The questions used in each survey showed some problems in consistency and appropriateness. Major issues identified are as follows. First, the questions in each survey were not consistent, and would be inappropriate to make time series comparisons. Second, the purpose of physical activity was not clear. Third, the examples of physical activities suggested in the questions were not appropriate. Fourth, the intensity of physical activity were not adequately described. Fifth, by excluding walking from the moderate-intensity physical activity category, the prevalence of moderate-intensity physical activity could be underestimated. Sixth, it is difficult to measure the total amount of physical activity performed in one day because answers from the other domains cannot be clearly differentiated. Conclusions: The physical activity questions in the KNHANES questionnaire should be improved so that they are consistent with the purpose of survey, the respondents can easily understand the contents of the questions, and the questions can measure all physical activity performed in the different domains.