Abstract: In order to develope 99 Tc m complexes for 5 HT 1A receptor imaging agents, the compounds 1 (2 methoxyphenyl) 4 (2 mercaptoethyl) piperazine (MPMEP) as a monodentate, N, N bis(2 mercaptoethyl) N', N' diethyl ethylenediamine (BMPDEEDA) and N, N bis(2 mercaptoethyl) benzylamine (BMPBA) as tridentate are synthesized and characterized by IR, 1HNMR.Two compounds 99 Tc mO(MPMEP)(BMPDEEDA) and 99 Tc mO(MPMEP)(BMPBA) complexes have been prepared via "3+1" mixed ligand approach by using 99 Tc m glucoheptonate as precursor. Monodentate and tridentate concentration, reaction time, pH and temperature of the reaction system are optimized to achieve high labelling yield: pH=6.0～7.0, reaction temperature 60～70 ℃ and reaction time 20～30 min,the labelling yield of the 99 Tc mO(MPMEP)(BMPDEEDA) and 99 Tc mO(MPMEP)(BMPBA) are 95% and 90% after extraction by CH 2Cl 2. The reaction mixture is analyzed and separated by HPLC system, the radiochemical purity is more than 98%. Biodistribution of two 99 Tc mmixed ligand complexes in mice demonstrated that they can penetrate the blood brain barrier and have a high brain uptake and retention for a certain time in brain. The ratio of brain and blood uptake is 0.32 and 0.19 after administration 60 min for 99 Tc mO(MPMEP)(BMPBA) and 99 Tc mO(MPMEP)(BMPDEEDA). The radioactivity clearance from blood of 99 Tc mO(MPMEP)(BMPBA) is rapid, but the radioactivity level in blood is even high.