Lanreotide, a synthetic octapeptide analog of a native hormone somatostatin, was labeled with 131I, the most widely used therapeutic and easily available radionuclide. Radioiodination of Lanreotide was carried out by Chloramine-T and Iodogen methods. Chloramine-T and Iodogen were used as oxidizing agents to form an electrophilic iodine species, which then labeled the tyrosine of Lanreotide. The maximum radiolabeling yield was ∼80%. Chloramine-T was found more suitable than the Iodogen method, because nearly 25% of the initial iodine activity was lost/adsorbed on the Iodogen coating. Thin layer and high performance liquid chromatographies were used for monitoring the reaction of 131I with Lanreotide, the stability and purity of 131I-Lanreotide.