PROBLEM TO BE SOLVED: To provide a means as a method for producing an organic iodine-containing composition that allows the addition reaction of iodine with a liver oil to proceed moderately and efficiently, suppresses an oxidation reaction and a polymerization reaction due to rapid exothermic heat, prevents the thickening of the product and can remarkably reduces the by-production of resin-like sludge.SOLUTION: A liver oil of cartilaginous fish is heated to a temperature of not less than 30°C to less than 113.7°C and the addition reaction is carried out by adding solid iodine in a ratio of 1-15 pts.mass based on 100 pts.mass of the liver oil to the liver oil under agitation.
