The purpose of this work was to determine the nature and composition of the deeply colored complex (530 nm, smax = 2860) which is formed in solutions of cyanamide and pentacyanoammineferrate(II) ion. Initial studies of these solutions revealed the existence of an isosbestic point at 434 nm indicating that the color is probably formed by a simple two component system. Mole ratio and slope ratio studies demonstrated that the ratio of [Fe(CN)5NH3]3-/H2NCN is approximately 2. In view of the alkaline conditions ofof cyanamide is the coordinated species in the complex, and the following dimeric structure is suggested: [Fe(CN)5NCN(CN)SFe]8-. Its large molar absorbtivity indicates that it i probably a charge transfer complex.