Oxygen atom transfer reactions between cis-dioxomolybdenum(VI) complexes and tertiary phosphine have been paid much attention as model reactions of molybdenum oxotransferases such as sulfite oxidase and formate dehydrogenase. We have investigated the kinetics of the oxygen atom transfer reactions between cis-dioxobis(dithiocarbamato)molybdenum(VI) complexes [MoO 2 (RR dtc) 2 ] and PPh 3 and found that the nature of substituents on dithiocarbamates significantly influences to the reactivity of [MoO 2 (RR dtc) 2 ) 2 ]. In this study, we prepared a cisdioxomolybdenum(VI) complex with quadridentate dithiocarbamato ligand Bz 2 endtc 2 - (FIGURE 1), whose molecular formula seems to be written as [(MoO 2 (Bz 2 endtc)) 2 ], and investigated oxygen atom transfer reactions between the complex and PPh 3 .Oxygen atom transfer reactions between the complex prepared in this study and PPh 3 proceed simply to form μ-oxomolybdenmum(V) complexes. This behavior is in contrast to the fact that the oxygen atom transfer reactions between cis-dioxomolybdenum(VI) complexes with ordinary bidentate dithiocarbamato ligands and PPh 3 proceed as follows: The remarkable behaviors of oxygen atom transfer reactions of the complex prepared in this study seems to be owing to the structural factor of Bz 2 endtc 2 - .