Six new dioxobridged binuclear complexes of the type [MO(L)Z](2)Z, where M=niobium(V) or tantalum(V), L=N-alkylphenothiazines (NAPs) and Z=tartrate and oxalate for niobium and tantalum respectively, were synthesized. The stoichiometry of the complexes was proposed on the basis of elemental analyses, molar conductance, magnetic and thermal data. The coordination behaviour of the ligands was determined with the help of spectroscopic studies. The fungicidal activity of the complexes was evaluated.