Using the data of conductivity-temperature-depth (CTD) intensive observations conducted during Oct.-Nov.2005,this study provides the first three-dimension quasi-synoptic description of the circulation in the western North Pacific.Several novel phenomena are revealed,especially in the deep ocean where earlier observations were very sparse.During the observations,the North Equatorial Current (NEC) splits at about 12°N near the sea surface.This bifurcation shifts northward with depth,reaching about 20°N at 1 000 m,and then remains nearly unchanged to as deep as 2 000 m.The Luzon Undercurrent (LUC),emerging below the Kuroshio from about 21°N,intensifies southward,with its upper boundary surfacing around 12°N.From there,part of the LUC separates from the coast,while the rest continues southward to join the Mindanao Current (MC).The MC extends to 2 000 m near the coast,and appears to be closely related to the subsurface cyclonic eddies which overlap low-salinity water from the North Pacific.The Mindanao Undercurrent (MUC),carrying waters from the South Pacific,shifts eastward upon approaching the Mindanao coast and eventually becomes part of the eastward undercurrent between 10°N and 12°N at 130°E.In the upper 2 000 dbar,the total westward transport across 130oE between 7.5oN and 18oN reaches 65.4 Sv (1 Sv=10-6 m3s-1),the northward transport across 18oN from Luzon coast to 130oE is up to 35.0 Sv,and the southward transport across 7.5oN from Mindanao coast to 130oE is 27.9 Sv. Using the data of conductivity-temperature-depth (CTD) intensive op- tivaratory work during Oct.-Nov. 2005, this study provides the first three-dimension quasi-synoptic description of the circulation in the western North Pacific. Overview of novel phenomena are revealed, especially in the deep ocean where earlier observations were very sparse. During the observations, the North Equatorial Current (NEC) splits at about 12 ° N near the sea surface. This bifurcation shifts northward with depth, reaching about 20 ° N at 1 000 m , and then remains nearly unchanged to as deep as 2 000 m. The Luzon Undercurrent (LUC), emerging below the Kuroshio from about 21 ° N, intensifies southward, with its upper boundary surfacing around 12 ° N. Flash there, part of the LUC separates from the coast, while the rest continues southward to join the Mindanao Current (MC). The MC extends to 2 000 m near the coast, and appears to be closely related to the subsurface cyclonic eddies which overlap low-salinity water from the North Paci fic.The Mindanao Undercurrent (MUC), carrying waters from the South Pacific, shifts eastward upon approaching the Mindanao coast and eventually become part of the eastward undercurrent between 10 ° N and 12 ° N at 130 ° E.In the upper 2 000 dbar , the total westward transport across 130oE between 7.5oN and 18oN reaches 65.4 Sv (1 Sv = 10-6 m3s-1), the northward transport across 18oN from Luzon coast to 130oE is up to 35.0 sv, and the southward transport across 7.5oN from Mindanao coast to 130oE is 27.9 Sv.