Phytoplankton is a biotic community that together with phytobenthos, constitutes the base of aquatic trophic webs, being responsible for most of the primary oceanic production. Knowledge about its composition makes it possible to complement water quality evaluations as microalgae are excellent indicators of environmental conditions. In this study, it was proposed to analyze the community structure of microphytoplankton and its association with physical and chemical variables of the coastal zone between Cabo Codera and Paparo, including two important rivers, in Brión municipality of Miranda state. Phytoplankton samples were taken with trawls and bottles at six stations from April 2010 to April 2011 to estimate the composition and abundance of microalgae. Physical and chemical variables of the water were estimated. A total of 140 species were identified, distributed in diatoms (66%), dinoflagellates (27%), chlorophytes (2%), cyanobacteria (2%), euglenophytes (2%), and flagellates (1%). A distribution of organisms defined by the continent-ocean pattern was observed, in which the fluvial stations were mostly represented by diatoms, while a high percentage of dinoflagellates was observed in the marine stations in some months. The richness and biodiversity index were higher in the marine stations than in the fluvial ones. It was observed that the coastal upwelling influences the distribution of the marine microphytoplankton during the first months of the year, while in the high rainfall season, the contribution of the rivers influences its composition.