The presence of fragments or pieces of large plastic or macro plastic in the marine environment have generated great concern worldwide given its persistence in the environment. Due to the degradation suffered by these materials, there is contamination by microplastics and problems in the marine ecosystem. Nowadays, the sources of income of these pollutants to water bodies and their global dissemination have been investigated. It is important to perform an analysis about the abundance of microplastics in marine sediments and surface waters in order to obtain a clearer understanding of the availability of microplastics in the marine environment and the risks they pose to the health of the aquatic ecosystem and affect the ecological processes. Given the lack of information on microplastic contamination in the Gulf of Nicoya, there is a need to conduct a study that defines a baseline and contributes to diagnose the current situation of this environmental problem, as a first step towards reducing pollution marine by plastic waste in the Costa Rican Pacific Sea. For this study, it is necessary to sample sediment and seawater; then proceed to perform the laboratory analysis by means of density techniques and electron microscopy in order to quantify and characterize microplastics at various points in the study area.