Based on the grain size and rare earth elements (REE) geochemical data of the core C-P19 from the southeastern Parece Vela Basin and the core L3 from the south slope of the Mariana Trench in the western Pacific Ocean, we summarized and discussed in this paper both the similarities and differences in provenances between the sediments in the two places. Our study suggests that no obvious correlation between REE content and grain size of the sediments is observed in the study area, and the composition and distribution patterns of the rare earth elements are mainly constrained by provenance. The provenance discrimination results reveal that the sediments in the Parece Vela Basin and on the south slope of the Mariana Trench are homologous, and contributed mainly by the volcanic materials eroded from the western Mariana Ridge. Heavy minerals in volcanic materials may affect the content of rare earth elements. For example, the correlation coefficient between the content of zircon and the ∑REY is as high as 0.86. The terrigenous eolian dusts of loess from Chinese inland also contribute some to the sediment of the study area, but is not substantially. Since the south slope of the Mariana Trench is far away from the mainland and located in lower latitude, it receives little Asian dust comparing to the Parece Vela Basin and Challenger Deep. In addition, the Antarctic Bottom Water passing through the study area has certain impact on the sediments of the basin and trench, and is more active in the south slope of Mariana Trench. Therefore, the sediment deposited in the southeastern Parece Vela Basin is relatively easier to be preserved than that on the south slope of Mariana Trench.