Aqueous Fe­(II) can induce recrystallization of ferrihydrite and goethite [α-FeOOH] to their more crystalline or molecularly homogeneous counterparts. Despite common association with these and other Fe­(III) (oxyhydr)­oxides, relationships between Fe­(II)-induced transformation and Mo mobility remain poorly constrained. We conducted laboratory column experiments to examine repartitioning of sorbed Mo during Fe­(II)-induced transformation of ferrihydrite and goethite under advective flow conditions. We first pumped (∼0.25 L d–1) artificial groundwater containing 0.1 mM MoO4 2– and buffered to pH 6.5 through columns packed with ferrihydrite- and goethite-coated sand until >90% Mo breakthrough was observed. Extended X-ray absorption fine structure (EXAFS) spectroscopy shows that initial Mo attenuation resulted from inner sphere complexation of MoO4 tetrahedra at ferrihydrite and goethite surfaces. We then pumped Mo-free anoxic artificial groundwater containing 0.2 mM or 2.0 mM Fe­(II) through the columns until effluent Mo concentrations remained <0.005 mM. Raman spectroscopy shows that Fe­(II) introduction induced transformation of both ferrihydrite and goethite to lepidocrocite. Additionally, Fe­(II) introduction mobilized 4–34% of sorbed Mo and total mass release was greater for (i) ferrihydrite compared to goethite columns and (ii) low Fe­(II) compared to high Fe­(II) influent. Effluent pH decreased to ∼5.8 for columns receiving the high Fe­(II) influent and returned to pH 6.5 after 5–10 pore volumes. EXAFS spectroscopy indicates that structural incorporation of MoO6 octahedra into neoformed phases contributes to Mo retention during Fe­(II)-induced transformation. Our results offer new insight into Mo repartitioning during Fe­(II)-induced transformation of Fe­(III) (oxyhydr)­oxides and, more generally, controls on Mo mobility in geohydrologic systems.