Abstract The behaviour of Co-60 was comprehensively studied in a marine microhabitat in the presence of Cs-137, Cs-134, Zn-65, Fe-59 and Mn-54 by appling artifical modeling.The result showed that after getting into sea water, Co-60 was rapidly adsorpted by suspen sates and phytoplanktons. The concentrative ability of sediments for Co-60 was very low, its concentration coefficient was 3—4 in96 hr. The distribution of Co-60 in marine organisms and biochemical materials was studied at the same time. The critical organs for concentrating Co-60 were liver(or digestive-g'and) and stomach-intestine. The Co-60 in the great majority of biochemical materials can be detected except organic acids.Co-60 is mainly distributed in lipid, then in protein. After excretion experiment, the loss of Co-60 in stomach-intestine and biochemical materials was marked.However, the remain of Co-60 in liver(or digestive-gland) and protein of Arca subcrenata was 50% and 83% respectively. The concentration coefficient of Co-60 in sediments was 1—10 times compa red with the original.