Abstract: The distribution of total organic phosphorus (TOP),total organic nitrogen (TON),and dissolved inorganic nutrients in the middle-to-low latitude zone of the North Pacific was studied.In general, TOP and TON vary from 0.04 to 1.44 μM,and 0.13 to 26.61 μM respectively.TOP and TON are the major components of TP and TN in the surface water,accounting for 57.5%~94.2% of TP and 75.0%~98.4% of TN respectively,with highest concentrations in the surface water and lowest concentrations in the deeper water.TN:TP ratios in seawater at the stations near 20°N fluctuate around the Redfield ratio, indicating that the primary productivity in this region was limited by other factors instead of nitrogen and phosphorus.The TN:TP ratios in the water column near 10°N were significantly lower than the Redfield ratio,indicating that nitrogen was limited in this region.The joint physical and biological processes control the distribution of TOP and TON in surface water,and biological N2 fixation may play important role in the nitrogen cycle in the region.