Abstract: In recent years, plastic pollution has become a major global environmental issue. Nanoplastics in the ocean can be easily ingested by marine organisms and enrich in vivo, causing toxic effects to organisms. Nanoplastics can even be transferred through the food chain, threatening the health of marine ecosystem. In this study, polystyrene nanoparticles with different functional groups were used as research subjects, and the filter-feeding marine bivalve Paphia undulata was used as the test organism. The accumulation and distribution characteristics of nanoplastics in the tissues of the bivalves were analyzed after exposure to carboxylated- and amino-polystyrene nanoparticles (80 nm, 500 μg/L) for 48 h. The effects of different types of nanoplastics on the oxidative stress and damage in the tissues were also investigated. The results showed that both carboxylated- and amino-polystyrene nanoplastics could accumulate in the gill, mantle, digestive gland and gut of P. undulata, with the digestive gland being the most accumulated organ, followed by the gut, and the mantle and gill being less enriched. In addition, different functionalized polystyrene nanoplastics could cause oxidative stress and lipid peroxidation damage in P. undulata.