Abstract: Marine microplastic (MP) pollution has become a global concern. It was reported that the content of MPs in intertidal zone was relatively high. However, relatively few studies have been conducted on the effects of MPs on organisms inhabiting intertidal zones. In this study, we investigated the ingestion, bioaccumulation and egestion processes of fluorescent polystyrene microspheres (PS, 10 μm) in sediment-dwelling organism, Perinereis aibuhitensis, through seawater exposure pathway. The impacts of PS on the burrowing behavior and subcellular structure alteration of worms were also explored after a 14 d of sediment exposure. Results showed that the ingested PS microspheres in worms increased with time within 48 h, and the retained PS percentage decreased after transferring to clean seawater, which reached to only 2.2% after depuration of 96 h. However, the burrowing time of worms in clean sediment was significantly prolonged after 14 d of sediment exposure, and epithelia apoptosis of worm body wall and mitochondria edema of worm myocytes were observed. The impairment of worm burrowing behavior was possibly related to the dysfunction of mitochondria. This study emphasized the sensitivity of behavior indicator when assessing the toxicity of MPs on sediment-dwelling organisms. Findings are expected to provide a basis for exploration of mechanisms of MPs and their ecological risk assessment.