We have studied the interactions of REEs (La, Ce, Pr, Nd, Sm, Eu, Gd, Tb, Dy, Ho, and Er)-desferrioxamine B (DFO) complexes with Pseudomonas fluorescens cells and with gamma-Al2O3, at pH 4-9. Higher adsorption of REEs was obtained at lower pHs on P fluorescens cells and at higher pHs on gamma-Al2O3. The degree of negative anomaly of Ce compared to its neighboring REEs, La(III) and Pr(III) increased with increasing pH. XAFS analysis showed that Ce exists as the Ce(IV)-DFO complex in pH higher than 6. Thus, the pH dependence of Ce anomaly is predominantly dependent on the stability of Ce(IV)-DFO complex.