Abstract: Formation Energy of the nine TcON2S2 complexes has been studied by CNDO/2 calculation. The computed results of these complexes considered indicated that the order of formation energy (Et), a reflection of the in vitro stability, was parallel to that of the SAS values which has been proposed previously by using corn packing model method. The structure-stability relationship of TcON2S2 complexes using a stability indicator formation energy values is an alternative potential method for predicting stability and designing new 99Tcm radiopharmaceuticals,especially considering the second order effect which was produced by coordinated indirective atoms or groups in TcO-complexes. Net charge and formation energy of the nine TcON2S2 complexes based on X-ray crystallography data are presented in tables( 1 ) and (2). The results suggest that the CNDO/2 calculation method may be useful to aid the design of new 99Tcm radiopharmaceuticals.