Abstract: Based on water quality surveys conducted in Xiamen waters in October 2015 （autumn） and January 2016 （winter）， the temporal and spatial distribution of dissolved organic nitrogen （DON）， the composition of total dissolved nitrogen （TDN）， the correlation between DON and environmental factors and the sources are studied and discussed. The results show that the average concentration of DON is higher in winter than autumn and DON is higher in surface than bottom showing a higher DON in the bay and estuary and lower in offshore. DON concentrations distribute in order of Tongan Bay>West waters>Jiulong River Estuary adjacent waters>Southeast waters>Dadeng waters in autumn and West waters>Tongan Bay>Jiulong River Estuary adjacent waters>Southeast waters>Dadeng waters in winter. The ratio of C_DON/C_TDN in autumn and winter is 56% and 53%， respectively and is generally high in offshore waters than the waters in estuary and inner bay. The analysis showed a significant negative correlation between DON and salinity in autumn and winter and significant positive correlations with phosphate and silicate content. Besides， it correlates with chlorophyll a， dissolved oxygen and pH. The source of DON in Xiamen waters is mainly from terrestrial input of Jiulong River， urban sewage， industrial and agricultural wastes besides the phytoplankton activities．