In the North Pacific Subtropical Gyre (NPSG), one of the largest oligotrophic regions, information on material sources and transport by water mass mixing is lacking. Rare earth elements (REEs) can trace the sources and transport of trace elements and quantify the contribution of water mass mixing to the material. Here we present dissolved REE concentrations and their controls in the northwest Pacific during a China GEOTRACES cruise (GP09). In the surface water along 11 °N, we observed an input signal from the Hawaiian Islands and the Philippines Islands based on a positive Eu anomaly. In North Pacific Tropical Water (north of 11 °N), REEs in the upper water column (< 160 m) are not conservative, while slightly deeper (160-300 m) REEs are predominantly controlled by water mass mixing. In North Pacific Intermediate Water (potential density 26.0~27.2 kg/m³), non-conservative REEs added due to in-situ remineralization processes account for 46 ± 5 % and 71 ± 4 % of the Nd, and 59 ± 2 % and 82 ± 2 % of the Yb at σ_θ= 26.0 kg/m³ and σ_θ = 27.2 kg/m³, respectively. Low REE concentrations were consistently found in Antarctic Intermediate Water (AAIW) throughout the study area, and the intrusion of AAIW reached ~25 °N in the North Pacific along a potential density of 27.2 kg/m³. In deep water (>2000 m), we quantify the fractions of different water masses with a multiple-parameter mixing model using REEs along with salinity and potential temperature, and find that 70% -100% of the Nd and 80%-100% of the Yb are contributed by water mass mixing in the Northwest Pacific. Non-conservative REEs originate from the remineralization and dissolution of sinking particles (organic matter and siliceous particles). Weakly negative Ce anomalies are observed at ~1000 m water near the Philippine Islands, suggesting the input from slope sediments along with the steady anticyclonic eddy. Hydrothermal activity has negligible contribution to the concentrations of REEs and REEs anomaly in the study area. Our findings indicate that REEs provide valuable information about water masses transport, biological processes and lithogenic inputs (such as volcanic islands and sediments) in the oligotrophic ocean.