Two chromium(III)–cysteine complexes, [Cr(Cys) 2 ] − and [Cr(Cys)(H 2 O) 3 ] + , have been synthesized, and their reactivity in aqueous solution studied. Kinetics of the acid-catalyzed Cr–S bond fission was studied in strongly acidic medium, monitoring the absorbance decrease of the S → Cr CT band. The dependences of the pseudo-first-order rate constants on [H + ] were determined. The spontaneous Cr–S bond cleavage in [Cr(Cys) 2 ] − was studied in alkaline medium monitoring the spectral changes within the d–d transition bands. Based on the obtained kinetic and spectroscopic data, a reaction mechanism is proposed and factors controlling the rate of Cr–S cleavage are discussed.