The release of anthropogenic radiocesium to the North Pacific Ocean (NPO) has occurred in the past 60 years. Factors controlling Cs (half-life, 30.2 year) and Cs (half-life, 2.06 year) activity concentrations in the Kuroshio east of Taiwan and the Taiwan Strait (latitude 20° N-27° N, longitude 116° E-123° E) remain unclear. This study collected seawater samples throughout this region and analyzed Cs and Cs activity concentrations between 2018 and 2019. A principal component analysis (PCA) was performed to analyze the controlling factors of radiocesium. Results of all Cs activity concentrations were below the detection limit (0.5 Bq m ). Analyses of water column Cs profiles revealed a primary concentration peak (2.1-2.2 Bq m ) at a depth range of 200-400 m (potential density σ 25.3 to 26.1 kg m ). The PCA result suggests that this primary peak was related to density layers in the water column. A secondary Cs peak (1.90 Bq m ) was observed in the near-surface waters (σ  = 18.8 to 21.4 kg m ) and was possibly related to upwelling and river-to-sea mixing on the shelf. In the Taiwan Strait, Cs activity concentrations in the near-surface waters were higher in the summer than in the winter. We suggest that upwelling facilitates the vertical transport of Cs at the shelf break of the western NPO.