Hydroponic experiments were conducted to study the effects of alginate oligosaccharides(AOS)on alleviating cadmium(Cd)toxicity in rice(Oryza sativa L),and to explore the physiological mechanism.The results showed that the pretreatments of different concentrations of AOS alleviated Cd toxicity in rice,with the treatment of 20 mg/L AOS having obvious effect,characterized by promoted rice seedling growth and increased photosynthetic pigment contents.Moreover,Cd content in shoots and roots and Cd transfer efficiency were significantly reduced due to addition of AOS,compared to only Cd treatment.The contents and proportion of Cd in cell wall of root were significantly increased.The contents of nonprotein thiols(NPT)in leaves and roots were increased by 23.5% and 14.9% respectively,and phytochelatins(PCs)contents were increased by 28.0% and 15.0%.The activities of antioxidant enzyme and the content of proline were also improved by AOS in varying degrees,and malonaldehyde(MDA)content was decreased by 27.1%.These results preliminarily indicate that these several mechanisms,including cell wall binding,chelation with intracellular thiols and antioxidant systems are involved in the alleviation of AOS on Cd toxicity in rice.