In this work, the photochemical degradation process of 17β-estradiol (E2) in a suspension of natural montmorillonite (NM) has been studied. The addition of the iron complexing agent ethylenediamine-N,N′-disuccinic acid (EDDS) to the suspension was investigated and compared with the system without EDDS. The effects of the main physicochemical parameters (pH, EDDS, oxygen and NM concentrations) on E2 degradation in NM suspensions were also investigated. In order to better understand the photochemical process, experiments were carried out in the presence of 2-propanol. In general, the photochemical efficiency of the E2 degradation is better in EDDS–NM suspensions than in NM suspensions, especially at higher pH. This work demonstrated that the NM–EDDS system is an interesting and valuable research area and could be considered as a promising photochemical system for wastewater treatment.