Actinium-225 (Ac-225) is a synthetic isotope of actinium with significant applications innuclear medicine, particularly in targeted alpha therapy (TAT) for cancer treatment. Ac-225,with a half-life of 10 days, undergoes a decay sequence that emits highly energetic alphaparticles, making it effective for selectively destroying cancer cells while minimizing damageto surrounding healthy tissue. This paper examines the nature, production, and decay pathwaysof Ac-225, including its role in the 4n+1 neptunium decay series and artificial productionthrough high-energy proton spallation of thorium-232. Furthermore, it explores Ac-225’sbinding energy, decay characteristics, and the advantages of its daughter isotope, bismuth-213,in therapeutic applications. The use of radionuclide generators for Ac-225 production and itsintegration into radiopharmaceuticals is also discussed. Given its cytotoxic potential andability to selectively target tumors, Ac-225 represents a major breakthrough in nuclearmedicine, providing an effective alternative to traditional cancer treatments.