Mesoscale eddy properties in the northwestern subtropical Pacific Ocean are investigated by analyzing 22,567 cyclonic eddies (CEs) and 26,365 anticyclonic eddies (AEs) detected from 19 year altimetric sea level records. Eddy occurrence frequency and kinetic energy are prevailingly high in the Subtropical Countercurrent zonal band between 19°N and 26°N and further elevated near the Luzon‐Taiwan coast. A general superiority of AEs is observed at most latitudes except between 19°N and 22°N, where the CE number is larger. The modal radius and mean lifespan of the CEs (AEs) are 134 km and 11.2 weeks (121 km and 10.9 weeks), respectively. After generation, most eddies propagate westward with a mean speed of 7.2 cm s⁻¹ and deflect northward following the Kuroshio along the Luzon‐Taiwan coast. Three‐dimensional eddy structures are further explored with composite eddy images in five subregions constructed by surfacing Argo temperature/salinity data into altimeter‐detected eddy areas. Due to the existence of mode waters in the main thermocline, eddy‐induced temperature anomaly exhibits a double‐core vertical structure which is especially evident in CE images. Because of the vertical water mass distribution, salinity anomaly features a sandwich‐like pattern which is more evident in AE images. Also revealed is the significant structure difference in these five subregions. Eddies are greatly intensified as they approach the western boundary, inducing larger temperature and salinity anomalies and influencing deeper ocean. Along the Luzon‐Taiwan coast, AEs are preferentially strengthened by the northward background flow.