<p>The rhenium-osmium (Re-Os) isotope system is a powerful tool for dating organic-rich sedimentary rocks, yet the mechanisms of Re and Os uptake and their fractionation in different types of organic matter remain poorly understood. Here, we investigate the role of terrestrial organic matter (e. g., wood of the species <i>Taxodium distichum</i> and charcoal generated from the same species in the laboratory) in Re and Os enrichment and isotope fractionation through laboratory experiments. The results show that charcoal has a significantly higher capacity to uptake both Re (68–77 times greater) and Os (1.7–2.2 times higher) compared to wood, with charcoal preferentially accumulating Re over Os, leading to higher ¹⁸⁷Re/¹⁸⁸Os ratios. These findings highlight the important contribution of terrestrial organic matter, particularly charcoal, to Re and Os concentrations and isotope fractionation in shales, and the importance of organic matter type for chelating Re and Os as previously discussed. Furthermore, we discuss the potential of using Re to track organic carbon weathering, noting that the coupled release of Re and organic carbon during weathering provides new insights into carbon cycling processes.</p>