Adsorption of 153Sm-EDTMP and effect of several coexisting substances on adsorption and desorption were investigated using hydroxyapatite （HA） as a skeleton model and 153Sm as a tracer. The adsorption is shown to be quantitative up to total deposition of 40 μmol/（g HA）

while non-quantitative when the complex concentyation is >40 μmol/（g HA）

in the medium of pH=7.0±0.2. The uptake increases significantly with the addition of Ca2+ ions. The ability to desorb the adsorped complex is in order of EDTMP>> DTPA > EDTA. Two adsorption modes of 153Sm-EDTMP on HA are suggested

i.e. （1） quantitative （when the amount of adsorbed complex is ≤ 40 μmol/（g HA））

and （2） less efficient （>40μmol/（g HA））.Non-quantitative adsorption is attributed to Coulomb repulsion while the complex amount is ranging from 40 to 80 μmol/（g HA）.