Abstract: The method of the preparation of β methyl p iodophenyl pentadecanoic acid(BMIPP) is developed. The synthesis and physical properties of BMIPP are described. BMIPP is characterized by IR, 1 HNMR, elementary analysis and MS. 125 I BMIPP can be easily prepared by two methods: direct labelling and iodo exchange labelling. The lablling yield is 80% confirmed by TLC, and the radiochemical purity is higher than 98% after extaction.