Abstract: Objective To evaluate the feasibility and stability of chloramine-T labeling of somatostatin analog Tyr-oetreotide, observe its biodistribution in mice.Methods ¹³¹Ⅰ-Tyr-octreotide was prepare for chloramine-T method and the radiochemical purity and colloid content were measured and the biodistribution was studied. ¹³¹Ⅰ-Tyr-octreotide was injected via tail vein and measure the radioaction of differents organs at differtent time.Results The best condition of ¹³¹Ⅰ-Tyr-octreotide labeling was:(0.2 mol/L) 0.15 ml H₃PO₄ buffer, Tyr-octreotide (1 g/L) 10 μl, Na¹³¹Ⅰ(3.7 MBq)0.1 ml, chloramine-T (30g/L)4μl, Na₂S₂O₅ (30g/L)5μl, reaction time is 2.5 min. The instant radiochemical purity was (97%), and the radiochemical purity of (83%) was remaind after 6h, colloid content is 1.02%. The biodistribution showed high uptake of the tracer in kidney and liver, the stomach intestine was also high, other organs show low uptake.Conclusions Tyr-octreotide was easy to be labeled by chloramine-T. It has achieved high radio-labelling ratio and is a convenient and fast methods. It was quickly cleared from blood and has a high target. ¹³¹Ⅰ-Tyr-octreotide may be a promising agent mediated by somatostatin for diagnos and treatment of cancer.