Host phase of lanthanum (La) in deep-sea rare-earth elements and yttrium (REY)-rich mud was directly determined by X-ray absorption fine structure (XAFS) and micro-focused X-ray fluorescence (mu-XRF) analyses. Excitation of K edge of La by high-energy X-ray allowed us to avoid severe interferences of coexisting elements such as vanadium and titanium in XAFS and XRF. It was revealed for the first time that La is accumulated in apatite in this type of sediments.