The purpose of this study was to define a portion size for dishes frequently consumed by Korean adults especially focusing on main dishes like rice, noodles, soups, and stews. From the original 8,019 people who took part in the Korea National Health and Nutrition Examination Survey (KNHANES) 2010, we analyzed the data for 4,556 persons aged 19 to 64 years and selected dish items consumed based on an intake frequency of 30 or more by all participants. The portion size of each dish item was set on the basis of the median amount ($50^{th}$ percentile) in a single intake by a single person. In the rice category, 15 items were selected, of which the most frequently consumed item was steamed rice with a portion size of 250ml. Among noodles and dumplings, the most frequently consumed dish was ramyeon with a portion size of 500ml. As for soups, the portion size was $250m{ell}$ for kongnamul guk and $300m{ell}$ for miyeoguk. In stews, the most frequently consumed items were kimchi jjigae followed by doenjang jjigae with a portion size of $200m{ell}$ and $125m{ell}$, respectively. In a comparison of portion sizes between the KNHANES 2010 and KNHANES 2005, the portion size of some noodles, soups, and stews tended to decrease from 2005 to 2010. Portion sizes established in this study for dish items consumed regularly by adults may be conveniently and effectively used in dietary planning, in nutritional education programs, and in assessing the dietary intake status of Korean adults.