Concentrations of particulate plutonium together with dissolved plutonium and the biogenic unique organic ligand (SOL) in particulate matter (PM) in surface and deep waters were determined in samples collected during the IAEA'97 cruise to the Pacific Ocean. Concentrations of particulate 2 3 9 , 2 4 0 Pu in the water column ranged from 0.04 to 0.28mBqm - 3 . The percentage of particulate 2 3 9 , 2 4 0 Pu to total 2 3 9 , 2 4 0 Pu in seawater was less than 10% in surface waters and less than 2% in deep waters. In order to characterize particulate 2 3 9 , 2 4 0 Pu in seawater, the relationship between particulate 2 3 9 , 2 4 0 Pu, dissolved 2 3 9 , 2 4 0 Pu and SOL concentrations in surface PM was examined. The results reveal that particulate 2 3 9 , 2 4 0 Pu in surface waters was linearly related to SOL concentration and independent of dissolved 2 3 9 , 2 4 0 Pu concentrations. On the other hand, particulate 2 3 9 , 2 4 0 Pu in deep waters does not seem to be related to the SOL concentration alone. pH values are discussed as another factor controlling particulate 2 3 9 , 2 4 0 Pu in deep waters. The results suggest that the dominant chemical form of 2 3 9 , 2 4 0 Pu in surface and deep PM, which may exist as Pu(IV), is a complex of SOL onto PM.