Binding properties of Fur protein to the operator region of aerobactin operon were investigated. By nitrocellulose filter binding assay, dissociation constant of Fur-operator complex was ranged 3∼6×10^(-12) M² using Mn^(2+) as a corepressor. Hill plot of the binding isotherm indicates that the repressor protein forms dimer in order to bind the operator. Stability of Fur-operator complex depends on the divalent transition metal involved in the complex. Binding affinity of the protein was not altered by the different incubation temperature. However, at higher temperature the repressor showed higher saturation level with the same amount of operator.