In order to explore the effects of extracellular polymeric substances (EPS) on the accumulation and migration of arsenic(As) in microalgae, EPS of Chlamydomonas reinhardtii were extracted with 1 mmol/L ethylenediaminetetraacetic acid(EDTA). The content and major components were determined and the cell viabilities after EPS removal were observed using LIVE/DEAD BacLight staining and laser confocal microscopy. The As absorption, adsorption and transformation by C. reinhardtii with and without EPS were compared under the AsV treatment(20 μg/L, 6.0 h). The results showed that the total EPS of C. reinhardtii was 16.12 mg/g, with primary component of polysaccharide(89.96%) and a small amount of protein (7.41%) and DNA (2.63%). The EDTA extraction did not cause cell lysis and did not affect the growth of C. reinhardtii. The AsV reduction by C. reinhardtii was significantly reduced after the removal of EPS. No significant change in the As absorption was found within 6.0 h, however, the ratio of As adsorption to accumulation of C. reinhardtii without EPS (43.03%-66.23%) was significantly higher than that with EPS(10.68%-31.90%), indicating that EPS may play an important role in the accumulation and transformation of arsenic by C. reinhardtii.