Abstract: Based on the chronostratigraphic framework established by ²¹⁰Pb, the organic carbon and its burial records over the past century were reconstructed by analyzing the Total Organic Carbon (TOC), Total Nitrogen (TN), stable carbon isotope (δ¹³C), and particle size of the core D1 sediments at the tip of Bangkok Bay, Thailand. The results showed that TOC and δ¹³C contents increased first, and then decreased toward the top. The results showed that the TOC content and δ¹³C values of the core D1 sediments varied from 1.35% to 2.26% and −24.18‰ to −22.67‰, respectively, both of which took on a bottom-up trend of increasing and then decreasing. The mangrove forests in the sampling area are estuary type. Compared with marine type mangrove forests, the source of organic carbon in sediments in the study area is less affected by mangroves, which is due to the fact that the light mangrove carbon debris is easy to be decomposed or carried to the open sea by the periodic high and low tides and the scouring of the runoff from the estuaries, making it difficult to be stored in sediments. Through a comprehensive analysis of environmental factors in the study area, terrigenous, marine and anthropogenic sources were selected as the three end members. The calculation results showed that the organic carbons in the core D1 sediments are mainly from anthropogenic and marine sources, and the contribution of terrestrial sources is relatively low. Since 1939, the organic carbon contribution of anthropogenic source has been increasing. From 1980 to 2008, the material flux into the sea decreased due to the construction of dams upstream of the rivers. In addition, the regional climate pattern was changed during this period, the rainfall was correspondingly decreased, and the contribution of terrestrial organic carbon was relatively reduced. Moreover, due to the enhancement of human activities such as reclamation and aquaculture, the contribution of anthropogenic organic carbon has increased relatively. During the period, mangrove forests were cut down on a large scale, weakening its role of coastal barrier at the sampling locations and increasing the contribution of marine organic carbon in sediments. Since 2008, the organic carbon contribution of terrigenous source has almost disappeared due to the restoration of mangrove forests and the construction of dykes.