The middle Eocene is a key time period for understanding Cenozoic cooling of the global climate. In eastern Asia, this time period was marked by deposition of extensive mudstones, shales and interbedded siltstones, especially in the midlatitude Bohai Bay Basin. Still, midlatitude terrestrial records of climate evolution during the middle Eocene are rare. Here, we analyze a continuous, high-resolution record of this period using samples of the shales in the fourth submember of the third member from the mid-Eocene Shahejie Formation (MES shales) in the Bohai Bay Basin using major-element and wavelet analysis. We use this information to derive insights into terrestrial paleoweathering and paleoclimatic evolution during the mid-Eocene in this midlatitude region. As a result of element mobility during continental weathering, the MES shales are more enriched in Ca and depleted in Na compared to average upper continental crust (UCC). The MES shales experienced moderate paleoweathering with limited K-metasomatism under a subtropical monsoon paleoclimate with mean annual temperature (MAT) of 8.3-12.9 °C and mean annual precipitation (MAP) of 685-1100 mm/yr. The MES shales record a mixed provenance involving intermediate igneous rocks, and low compositional maturity. The nutrient-rich environment led to enrichment in organic matter in the MES shales. We divide the depositional process of the MES shales into two stages that represent distinct climates. In stage I, the paleolake was high in nutrients, and the MES shales experienced high chemical weathering due to a relatively warmer and more humid climate. In contrast, the climate in stage II was relatively cold and dry, and the maturity of the MES shales was relatively high during this stage, suggesting a relatively stable tectonic background.