<p>The Oceanic Anoxic Event 1a (OAE 1a) represents one of the most significant environmental perturbations during the Cretaceous. During OAE 1a, changes in climate and ocean redox conditions exhibit noteworthy spatiotemporal heterogeneity. However, environmental changes in the Eastern Tethys during OAE 1a remain poorly constrained. In this study, high-resolution geochemical data of organic carbon isotope (δ¹³C_org), redox-sensitive trace elements (RSTEs), and total sulfur (TS) were used to correlate the OAE 1a interval of two sections in the Eastern Tethys: the Gucuo II section in Southern Tibet and the Ocean Drilling Program (ODP) Site 765C in the Argo Abyssal Plain. Paleoredox and paleoclimate proxies of these sections exhibit similar trends across OAE 1a, indicating synchronized environmental changes. RSTEs and TS contents increase before OAE 1a, remain elevated during OAE 1a, and decrease to near background values after OAE 1a, indicating preceding deoxygenation and prolonged reoxygenation in the Eastern Tethys. Weathering proxies, including the chemical index of alteration (CIA), chemical index of weathering (CIW), and Ti/Na ratios, exhibit a decreasing trend beginning before the onset of OAE 1a and continuing into early OAE 1a, followed by an increasing trend during late OAE 1a, indicating a delayed enhancement in weathering in the Eastern Tethys. Regionally, the delayed weathering enhancement might have resulted from dry climate and/or transient cooling episodes during early OAE 1a. This study elucidated the regional environmental response of the Eastern Tethys to OAE 1a, contributing to a more comprehensive understanding of the initiation and cessation mechanisms of OAE 1a.</p>