The manganese(V)-nitrido polyoxometalate derivative [PW11O39{(MnN)-N-V}](5-) has been synthesized by photochemical activation of the parent manganese(III)-azido derivative [(PW11O39MnN3)-N-III](5-) It was characterized by mass spectrometry, P-31 NMR, UV-vis, and IR spectroscopies. An electrochemistry study indicated that only the Mn(V) state was stable. The photoactivation of the manganese(III)-azido derivative proceeds through two competitive routes, yielding to the targeted product of photooxidation {(MnN)-N-V} or the undesirable product of photoreduction {(MnL)-L-II} (L = H2O, N-3) depending on the photolysis conditions. A simplified photolysis mechanism involving two different excited states was proposed to account for the temperature and wavelength dependence.