South China Sea (SCS) sediments can provide important paleoclimate records because of their generally high deposition rates and strong regional influence of East Asian summer monsoon (EASM) variations. However, interpretation of sedimentary records from the northwestern SCS slope is complicated because sedimentation is sensitive to sea level and provenance variations. We seek to develop a paleoclimatic record of SCS sediments by analyzing sediment magnetic properties over the past ∼36 kyr from core PC338. The dominant magnetic minerals are magnetite and hematite in most parts of the core. The hematite concentration increased profoundly over the ∼15–32 kyr B.P. period when sea level was lower than −90 m below the present level. This suggests that Red River inputs were enhanced significantly in this period. Moreover, increased coarse magnetite contents were recorded in association with an enhanced East Asian winter monsoon (EAWM) during the Last Glacial Maximum and Heinrich event 1. Low‐field and frequency‐dependent magnetic susceptibility variations were coeval with EASM‐controlled climate change recorded in South China and the SCS over the past 15 kyr, probably because regional terrestrial weathering and erosion of iron‐bearing minerals, and their transportation are dominated by climate. Rhythmic coarsening of Holocene magnetic mineral concentrations coincided with global cooling events, which indicates that core PC338 also contains signals of enhanced EAWM variations. The study demonstrates that magnetic proxies are indicative of sediment supply and deposition variations on the SCS continental slope that are useful for understanding the effects of sea level and climate change on SCS sediments.