The cutting dates of 10 wood timbers (girders and corner rafters) of Sinmu-mun, the north gate of Kyungbok Palace in Seoul, were determined by the dendrochronological method. Tree-ring chronologies of unknown dates derived from the timbers were crossdated using the graphic comparison method against the dated master chronologies derived from living trees. The living trees for the masters used for this study were Pinus densiflora Sieb. et Zucc. (Japanese red pine), a major timber species for Korean traditional buildings. By comparing the Sinmu-mun samples with the masters from the western Sorak Mountains in central-eastern Korea, the Sinmu-mun samples yielded the cutting dates A.D. 1868, 1869, and 1870/1871. Surprisingly, these dates are 3 to 6 year later than the known date (A.D. 1865) of the Sinmu-mun reconstruction, which was recorded in a historical document ‘Ilsungrok’, the King's official diary. Since the time that the Sinmu-mun construction date had been questioned, another record was found in the 1872 April issue of Ilsungrok, indicating the rebuilding of Sinmu-mun in the 1870s. Both pieces of evidence, from tree-ring dates and historic records, prove that the rebuilding of Sinmu-mun started after the Fall of 1870, but not later than April 1872. The results prove that tree-ring dating is a precise dating method and it can be applied to archaeological studies on Korean structures.