Microplastics (MPs) are particles smaller than 5 mm that do not degrade rapidly and can be ingested by marine organisms and can also be transferred to higher trophic levels, including humans. Therefore, it is of great importance to monitor the occurrence of microplastics in marine bivalves. This study aimed to evaluate the presence, shape, size and chemical composition of microplastics in the oyster Crassostrea gigas in an aquaculture area in Santo Antônio de Lisboa, located in the Santa Catarina North Bay, Brazil. Fifteen oysters were harvested and only five were analyzed, their soft tissues were extracted, digested with KOH at 10% (1:3) for 72 hours, and then a density separation was performed with NaCl (1.2 g/cm3). Subsequently, the samples were filtered through a membrane (8 μm) and analyzed under the stereoscopic fluorescence microscope and the transmission electron microscope coupled to an energy dispersive spectrometer (SEM/EDS). Forty-two microparticles with sizes from 261.54 to 3066.6 µm were found, the majority being fibers (97% of the total) and the remaining fragments. Five different colors were found among the microparticles, blue being the color that was most present especially in the fibers. Fourteen microparticles were analyzed under the SEM/EDS, and all presented a high peak in the carbon molecule (C), suggesting it as a polymer. Consequently, the number of MPs ranged from 2 to 4 MPs/oyster. The chemical composition found in the microparticles was compared with other studies and four possible types of polymers were found: PVC, PET, PP and PS. Furthermore, with SEM/ EDS analyzes it was possible to visualize cracks and grooves on the surface of the particles, which are most likely due to environmental exposure. These results allowed us to show the presence of microplastics in oysters C. gigas from an aquaculture farm.