Somatostatin (SST) is a short-lived peptide hormone that regulates the endocrine system. The main use of the derivatives of SST is to diagnose diseases related to growth hormone and to use against some forms of cancer that involve growth hormone. Also, SST suppresses gastric acid secretion, gallbladder contractions, and pancreatic enzyme secretion. In this study, two different bifunctional chelating agents were used to examine the changes in the biologic half-life of SST. For this purpose, first D-penicillamine (DPA) and diethylene triaminepentaacetic acid (DTPA) were used to label SST with Tc-99m and then radiopharmaceutical potential of three Tc-99m-labeled complexes, Tc-99m-D-PA, (TC)-T-99m-D-PA-SST, and (99m)TcDTPA-SST, were compared with each other. Quality control for each labeled complex was established by using radiochromatographic methods. The radiolabeled complexes maintained their stabilities for 5 hours. Then, biodistribution studies were performed on Albino Wistar rats independently for three complexes. The results demonstrated that (TC)-T-99m-D-PA-SST exhibited long-term uptake in organs, and its clearance took longer than the Tc-99m-DTPA-SST complex.