Abstract: As phytoplankton are indisputably a major component of many food webs, estimating their abundance, biomass and growth rate has been an essential component of marine studies. The aim of this study is to establish the effects of different nutrient pulses on the cell size and biovolumes in competetive experiments of marine phytoplakton that was cultured from natural seawater. The growth of natural pytoplankton populations taken from Izmir bay (Aegean sea, Turkey) was observed for 6 different nutrient pulse periods (4, 8, 12, 24, 48 and 96 h) and determined Chl a, mean cell sizes and biovolumes. Thallassiosira allenii (Takano), Chaetoceros sp. and Gomphosphaeria sp. were dominated all pulse periods during the batch culture experiment. Nutrient pulses <2 days will be able to limit the exponential growth rate of community markedly. Although, T. allenii and Chaetoceros sp. cells enlarged their biovolumes with the extension of pulse period, Gomphosphaeria sp. cells was not.