Abstract: The southwestern flank of the Carlsberg Ridge in the Indian Ocean exhibits distinctive pattern of aeolian dust deposition, offering valuable insights into the sedimentary characteristics of the region and its response to the Indian Ocean monsoon. Based on the CJ09-19 sediment core collected from the southwestern part of the ridge, analyses of clay minerals and grain size, and AMS ¹⁴C dating were conducted. The sources, evolutionary processes, and controlling factors of clay minerals in the southwestern Carlsberg Ridge over the past 27000 years (27 kaBP) were explored. Results show that the sediments of the core station were mainly calcareous ooze, with foraminifera as the main component. The average content of clay minerals was 23%, among which the clay minerals were mainly illite, followed by smectite, and less contents of kaolinite and chlorite, with a small amount of palygorskite. The clay minerals of the sediments were primarily derived from Arabian Peninsula and northeast Africa, and the downcore variability of clay mineral contents show that Core CJ09-19 could be divided into three stages. Stage I (26.9~19 kaBP): the clay minerals were mainly from mixture sources of Arabian Peninsula and northeast Africa; Stage II (19~11 kaBP): were primarily derived from Arabian Peninsula; and Stages III (11~0 kaBP): were mainly from the Arabian Peninsula and northeast Africa. The evolution of clay mineral sources during 27 kaBP was mainly controlled by the intensity of the southwest monsoon in the Indian Ocean. The study also showed that the ratio of palygorskite/illite could indicate the intensity of the southwest monsoon in the Indian Ocean, and could be used as a proxy to the India monsoon.