Abstract: Substitution of aquo – lingands from hexaaqouchromolum (III) ion by Cysteine (Hcys) has been studied Kinetically at [H+] of 1.0 x 10-2 mol dm-3. The calculated activation parameters ( H* and S*) have been compared with those of water – exchange and related anation reactions of haxaaquochromium (III) ion. The obtained results support an associated path SN2).