Uteroferrin (Uf) is a purple acid phosphatase for which the reduced [Fe II Fe III ] form of the enzyme is catalytically active in the hydrolysis of phosphate esters. The binuclear non-heme iron active site of the native reduced enzyme (1/2metUf) and its molybdate-and phosphate-bound forms have been studied with absorption (ABS), circular dichorism (CD), and magnetic circular dichroism (MCD) spectroscopies to probe their geometric and electronic structure. CD and MCD in the UV-Vis region give the tyrosine (phenolate) to Fe III charge transfer bands which probe the ferric center. CD and MCD in the NIR region probe the d-d transitions of both the Fe II and the Fe III centers. Variable-temperature variable-field (VTVH) MCD combined with EPR data are analyzed to determine the g values and energies of the ground state and the excited sublevels. These parameters are further interpreted in terms of a spin Hamiltonian model, which includes the zero-field splitting (ZFS) of Fe II and Fe III centers and the exchange coupling (J) between the irons due to bridging ligation. These ground and excited-state results confirm that both irons are six-coordinate with a µ-OH bridge. Anions bind to the active site in a bridging mode, which perturbs the ground and excited states of both iron centers. In particular, the exchange coupling decreases, µ-OH bridge f Fe II bonding strength increases, and the Tyr f Fe III donor interaction increases upon the phosphate binding. These results are correlated with the recent X-ray crystal structure of the kidney bean purple acid phosphatase, which contains an Fe III Zn II active site. These studies provide geometric and electronic structure insight into the hydrolysis reaction mechanism of this enzyme.