Abstract: In order to investigate the pharmacokinetic characteristics of technetium ⁹⁹Tc methylenediphosphonate injection (⁹⁹TC-MDP) in the blood of rats, the content of ⁹⁹Tc-MDP in the blood of rats at different time points was directly determined by inductively coupled plasma-mass spectrometry (ICP-MS), and the drug-time curve was fitted with DAS 2.1.1 software. The main pharmacokinetic parameters were obtained. The results showed that the pharmacokinetic properties of ⁹⁹Tc-MDP in the blood of rats were consistent with the characteristics of the three-chamber model, and the half-life of the distribution phase T_1/2α was 0.047 h, indicating that the drug was rapidly distributed in the body after entering the blood through the tail vein. The elimination phase half-life T_1/2β and T_1/2γ were 0.113 h and 37.349 h respectively, indicating that the drug was cleared slowly from the body. The results can provide reference for the study of ⁹⁹Tc-MDP pharmacokinetics in human