The complex formation between Mn(II) cations and N - 3 anions was studied in aqueous medium at 25 o C and ionic strength 2.0 M (NaClO 4 ). Data of average ligand number, n (Bjerrum's function), were obtained from pH measurements on the Mn(II)/N - 3 /HN 3 system followed by integration to obtain Leden's function, F 0 (L). Graphical treatment of data and a matrix solution of simultaneous equations have given the following overall formation constants of mononuclear stepwise complexes: β 1 = 4.15 +/- 0.02 M - 1 , β 2 = 6.61 +/- 0.04 M - 2 , β 3 = 3.33 +/- 0.02 M - 3 , β 4 = 0.63 +/- 0.01 M - 4 . A linear plot of log K n vs. (n - 1) shows no change in the configuration during complex formation. Slow spontaneous oxidation of solutions to Mn(III) occurs when the N - 3 concentration is greater than 1.0 M.