The distribution and seasonal change of phosphate, silicic acid and nitrate of Sagami Bay were studied from 1993 to 1994. The concentrations and the ratios of these three components in the waters located below the sub-surface layer were shown to be quite similar as those observed 15 years ago. This finding could be ascribed to the fact that the nutrients caused by the increasing coastal eutrophication to date are quickly washed out into the open ocean by the presence of a fairly strong current： the residence time of the waters in this bay being short. The nutrients in the euphotic zone were often depressed to less than the limiting level for phytoplankton growth when the seasonal thermocline set over. The potential importance of silicon for diatom growth was essentially sustained by the upwelling of silicic acid enriched sub-surface waters and/or by the river waters. It was thus concluded that the nutrient environments in Sagami Bay are still favorable for the maintenance of diatom ecosystems.