Weathering is a key process in the transfer of material from continents to the hydrosphere. A latosol profile in Zhanjiang, Guangdong Province, South China, formed through intense weathering of basalt, was studied to improve understanding of Ba isotopic fractionation during basalt weathering. Profile horizons were grouped into Ba-depleted and Ba-enriched layers (D- and E-layers, respectively) according to the mass fraction of Ba lost or gained from the weathered profile relative to bedrock. δ137/134Ba values in the soil profile ranged from −0.22‰ to +0.02‰, lower than those of the parent basaltic rock (0.03‰ ± 0.03‰). In the D-layers, Ba isotopic fractionation can be explained by Rayleigh fractionation, implying that heavy Ba isotopes are preferentially leached. The Rayleigh fractionation model is not applicable to the E-layers because they preferentially acquired isotopically light Ba isotopes during weathering. Results indicate a net loss of heavy Ba isotopes during strong weathering of basalt due to the precipitation of Fe Mn (oxyhydr)oxides and adsorption on secondary minerals. A mass-balance model indicates that the average δ137/134Ba value of materials leached from the weathered profile is ~0.08‰, slightly higher than that of the bedrock. This suggests a loss of heavy Ba isotopes into the hydrosphere during weathering of basalt, consistent with the enrichment of heavy Ba isotopes in river waters. Unlabelled Image • This study presents the first measurement of δ137/134Ba for a latosol profile formed by highly weathering of basalts. • δ137/134Ba of latosols varies from -0.22‰ to 0.02‰, lower than that of bedrocks (0.03 ± 0.03‰) and average continental crust. • Mass balance calculation shows δ137/134Ba of leachate from the latosols is ~0.08‰, well consistent with the adjacent river. • Heavy Ba isotopes are preferentially leached during continent weathering. [ABSTRACT FROM AUTHOR]