Since the development of sophisticated molecular carriers such as octereotides for peptide receptor targeting and monoclonal antibodies against various antigens associated with specific tumor types, radionuclide therapy (RNT) employing open sources of therapeutic agents is promising modality for treatment of tumors. furthermore, the emerging of new therapeutic regimes and new approaches for tumor treatment using radionuclide are anticipated in near future. In targeted radiotherapy using peptides and other receptor based tarrier molecules, the use of radionuclide with high specific activity in formulating the radiopharmaceutical is essential in order to deliver sufficient number of radionuclides to the target site without saturating the target. In order to develop effective radiopharmaceuticals for therapeutic applications, it is crucial to carefully consider the choice of appropriate radionuclides as well as the tarrier moiety with suitable pharmacokinetic properties that could result in good in vivo localization and desired excretion. Up to date, only a limited number of radionuclides have been applied in radiopharmaceutical development due to the constraints in compliance with their physical half-life, decay characteristics, cost and availability in therapeutic applications. In this review article, we intend to provide with the improved understanding of the factors of importance of appropriate radionuclide for therapy with respect to their physical properties and therapeutic applications.