Spatially and temporally resolved observations of precipitation water isotopes are essential for quantifying groundwater recharge, constraining hydroclimate variability, and calibrating paleoclimate proxies, yet such datasets remain scarce for monsoon-influenced volcanic islands characterized by steep topography and strong maritime and continental interactions. Here, we present a spatially resolved 39-month dataset (September 2000 to December 2003) of precipitation water isotopes (δ¹⁸O, δD, and d-excess) collected from 15 monitoring stations across Jeju volcanic island, South Korea, spanning elevations from 10 to 1,500 m above sea level. The dataset comprises 462 precipitation samples and captures pronounced seasonal variability together with island-wide spatial gradients. Monthly mean isotope values exhibit a distinct monsoon-driven seasonal cycle, with isotopic depletion during summer and enrichment during winter, which is well represented by sinusoidal fitting for δ¹⁸O and δD. Spatial analyses reveal a clear altitude effect, with mean lapse rates of −0.15 ‰ per 100 m for δ¹⁸O and −1.1 ‰ per 100 m for δD, while d-excess displays weaker elevation dependence but pronounced seasonal sensitivity to moisture source humidity and evaporation conditions. This dataset provides a robust observational basis for developing high-resolution regional isoscapes, estimating groundwater recharge elevations, and serving as benchmark input and validation data for isotope-enabled climate and hydrological models. All data are openly available with comprehensive metadata, enabling direct reuse in hydrological, climatological, and paleoclimate studies across monsoon-affected volcanic island environments.