We analyzed nitrogen isotopic ratio (δ15N) of settling particles at four sites in the western and central equatorial Pacific from January to November 1999, together with the δ15N of nitrate above 200 m depth in December 1999. The δ15N values of settling particles at the two western sites (station 1 and 2) were about 3.0 ? more depleted than that at the most eastern site (station 9). In March 1999, the δ15N values rose from 3.7 ? to 7.2 ? at station 3 located at 0¿N 145¿E. During this month, the salinity at this site also increased by 0.4 psu, suggesting that low-salinity water had shifted to the west. The relationship between salinity and δ15N of nitrate in surface water suggested that the depleted δ15N reflects river discharge, atmospheric deposition and/or nitrogen fixation. Thus, we were able to reconstruct the transition of low-salinity water in the WPWP based on the δ15N values of settling particles.