The sulfurization mechanism within contemporary marine oxygen-deficient zones promotes the preservation of organic matter. However, it remains to be investigated whether low sulfate concentrations in Mesoproterozoic and Early Cambrian oceans restricted organic matter sulfurization. This study examines the petrological characteristics, pyrite morphology, total organic carbon (TOC) and sulfur (TS), and organic sulfur components of source rocks of the Mesoproterozoic Xiamaling Formation and the Lower Cambrian Yuertusi Formation, employing thin section observation, chromium reduction method, scanning electron microscopy, elements analyzer, and X-ray photoelectron spectroscopy (XPS). The organic S: C atomic ratios in kerogen range from 0.7–5.8%. Organic sulfur species include aliphatic sulfurs, aromatic sulfurs, sulfoxides, sulfones, and sulfonates. The distribution of these species is controlled by redox conditions, TOC, and organic sulfur abundance. Results indicate that sulfurization could occur in settling particles and/or sediments within anoxic water columns, euxinic wedges at shelf edges, and restricted basins during the Mesoproterozoic and Early Cambrian.The process of organic matter sulfurization during these periods can be categorized into rapid sulfurization occurring within days at the anoxic water column and sediment–water interface, and slow sulfurization over millennia in the sediments. Anoxic environments prevalent during the Mesoproterozoic likely expanded the range of sulfurization. However, low sulfate concentrations may have limited the degree of sulfurization of organic matter during the Mesoproterozoic, with the maximum S: C atomic ratio not exceeding 3%. Studying organic matter sulfurization enhances understanding of organic carbon cycle fluctuations and the mechanisms of organic matter enrichment associated with oceanic anoxic events throughout geological history.