Preliminary studies on microzooplankton grazing were conducted with dilution method in Jiaozhou Bay from summer 1998 to spring 1999. Four experiments were carried out at St.5 located at the center of Jiaozhou Bay. Chlorophyll a concentrations were consistently dominated by netphytoplankton(net-,＞20μm), except during the autumn 1998 cruise, when they were dominated by nanophytoplankton(nano-,2-20μm). The contribution of picophytoplankton (pico-,＜2μm) to total chlorophyll a concentrations(＜200μm) varied considerably between cruises. Instantaneous growth coefficients(u) of phytoplankton varied from 0.098 to 1.947d-1, with mean value of 0.902d-1. Instantaneous coefficients(g) of microzooplankton grazing on phytoplankton ranged from 0.066 to 0.567d-1, mean value of 0.265d-1, which was equivalent to daily loss of 21.9% of the initial standing stock and 58.1% of the daily potential production.