To radiolabel bioactive molecules, we synthesized $^{99m}$Tc-tricarbonyl precursor, [$^{99m}$Tc(CO)$_3$($H_2O$)$_3$]$^{+}$ with a low oxidation state ( I ). The [$^{99m}$Tc(CO)$_3$($H_2O$)$_3$]$^{+}$ was prepared by low pressure carbonylation (1 atm of CO) of [$^{99m}$Tc $O_4$)]$^{[-10]}$ in the presence of NaB $H_4$ resulting in higher than 98% of labeling yield and stability up to 8 hrs. We evaluated the characteristics of $^{99m}$Tc- tricarbonyl labeled bioactive molecules by carrying out in vitro and in vitro study. Prepared [$^{99m}$Tc(CO)$_3$($H_2O$)$_3$]$^{+}$ was then reacted with some ligands of significance in modem diagnostic nuclear medicine and some amino acids. Labeling yields were checked by HPLC and found to be usually high, excluding $^{99m}$Tc-tricarbonyl-MDP, -EDTMP and -mIBG. And the biodistribution properties of $^{99m}$Tc-tricarbonyl complexes applied in rabbit showed different appearance comparing with that of the $^{99m}$Tc-labeling by conventional means. From these results, we conclude that [$^{99m}$Tc(CO)$_3$($H_2O$)$_3$]$^{+}$ is a potential precursor to. development ofecursor to. development off