The aim of this study is to prepare radiolabeled guanine with Tc-99m(CO) (3) (+) core. For this purpose, guanine has been radiolabeled with Tc-99m(CO) (3) (+) core. Quality control study of radiolabeled guanine molecule with Tc-99m(CO) (3) (+) core was performed by thin layer radio chromatography (TLRC) and high performance liquid radio chromatography (HPLRC). The results showed that the radiolabeling yield was quite high (94 +/- A 3%). Beside that Tc-99m(CO)(3)-Gua complex has showed good in vitro stability during the 24 h period. Radiopharmaceutical potential of this complex was evaluated in Wistar Albino Rats. It was concluded that Tc-99m(CO)(3)-Gua could be used as a nucleotide radiopharmaceutical for in vivo applications.