Abstract: With dilution technique, this paper studied the microzooplankton grazing rate (） and the phytoplanton growth rate (g） of Daya Bay in March, 2005. Grazing experiments were conducted at 5 stations within the Bay. The phytoplankton growth rate and microzooplankton grazing rate is about 0.16~1.14 per day, 0.33~1.74 per day, respectively. The percentage of microzooplankton grazing pressure on the phytoplankton standing crop is 47%~258% per day. And the percentage of potential primary production ingested by microzooplankton per day is about 70%~330%. The results showed that Daya Bay water isJP2 the typical subtropical water with high and g, and the herbivory of microzooplankton and growth of phytoplankton are also influenced by the currents and other factors. Compared with the similar studies in other bays around the world, the grazing pressure of microzooplankton in Daya Bay is at the higher levels.