Urea, dissolved organic nitrogen (DON) and dissolved inorganic nitrogen (DON) concentrations in waters of Hiroshima Bay, Etauchi Bay, northeast Suo Nada and the Ohta River were measured. Range and average concentration of urea were 0.08-3.32 (0.67) μg atNℓ-1 in Hiroshima Bay, 0.00-5.01 (0.85) μg atNℓ-1 in Etauchi Bay, and 0.15-2.50 (0.91) ,μg atNℓ-1 in Suo Nada, respectively. Although the range in urea concentration observed in the water of the Ohta River (0.23-3.15 μg atNℓ-1)was in the same level as those in the other coastal areas, the average value (1.49 μg atNℓ-1)was significantly higher than those in the other coastal areas. This means that the river inflow is one of the important supply source of urea for the coastal area. In the Ohta River water, DON (41.6 μg atNℓ-1 in the average) and DIN (30.7 μg atNℓ-1 in the average) concentrations were also high. Judging from the low Urea/DIN (%) in the Ohta River water, it was supposed that, compared to urea, DIN would be principal nitrogen source for the growth of phytoplankton in the estuary of Hiroshima Bay. The Urea/DON (%) observed in this study was 5.7-12.9%, which revealed the contribution of urea in the total DON load was not so high both in the river and the coastal waters. The distribution of urea in the coastal environments is heterogeneous, not showing any regular distribution, as has already been shown in several papers. However, the coefficient of varitaion was not always high in urea (34.2-89.4%) compared to those of DON (77.2-103.7%) and DIN (50.2-75.3%). From the Urea/DIN (%) in the three coastal areas (34.4-42.8%), the contribution of urea in all nitrogen forms (DIN+Urea) used for the primary production was estimated 7.2-8.4% in the average.