This dataset provides water stable isotope measurements (δ17O, δ18O, δ2H, d-excess, and 17O-excess) of precipitation collected in Seoul, South Korea, from January 2016 to December 2020. Precipitation samples were gathered biweekly in accordance with Global Network of Isotopes in Precipitation (GNIP) guidelines, with more frequent sampling during monsoon and typhoon events. The monthly means were calculated from these biweekly measurements, except for a sampling gap that occurred between March and June 2019. All isotope analyses were performed using a Picarro L2140-i cavity ring-down spectroscopy (CRDS) system. During the observation period, measured δ17O ranged from –9.62‰ to 0.61‰, δ18O from –18.21 ‰ to 1.15‰, and δ2H from –132.0‰ to +3.3‰. Corresponding d-excess values varied between –5.9 ‰ and 24.9‰, while 17O-excess ranged from –28 to +69 per meg. These data capture both seasonal and interannual variability in precipitation isotopes, offering insights into atmospheric moisture sources and transport pathways over the Korean Peninsula. This dataset will be valuable for studying hydrological processes, tracing moisture origins, and examining regional climate variability in East Asia. In particular, the inclusion of 17O-excess can advance the understanding of water cycle dynamics and provide fresh perspectives on the mechanisms driving precipitation in monsoon-influenced regions.