Abstract: The iodine ion-elective electrode method and neutron activation analysis combined with chemical separation were used to determinate total iodine and inorganic iodine from seaweed Laminaria japonica, The subtraction method was used to calculate the organic iodine.The average contents of iodine in Laminaria japonica could constitute 0.133% of fresh weight.The iodine contents vary greatly within the same sample.The front of Laminaria japonica was rich in iodine than the stipe, especially in the top of front, which the contents can reach 0.183 % .The root parts had the richer organic iodine( 13.9% in total iodine) than front parts.The total contents of inorganic iodine was 88%, the organic iodine was about 12%.