Stable carbon and nitrogen isotope analysis reveals the diets of different human populations in history. In this study, we performed stable isotope analysis on human skeletons from Joseon-period cemeteries discovered around Old Seoul City (Hansung). Our data clearly showed that Joseon individuals consumed more C₃-based than C₄-based foods as the main staples, and that the proteins they ate were mainly of terrestrial, but not of marine origin. Stable isotope values exhibited unique patterns in each of our sample subgroups. Whereas the δ¹³C values did not show any statistical differences among the subgroups, significantly higher values of δ¹⁵N were found in males than in females, which might reflect dietary differences between the sexes. For a fuller understanding of the dietary patterns of pre-industrial (pre-20th century) Koreans, additional studies on Joseon samples from Korean archaeological sites will be necessary.