A variety of new chemical sensors for determination of triple charged rare earth (RE) metal cations from lanthanum(III) to lutetium(III) (lanthanides) has been developed and studied. Well-known extractants-bidentate neutral organophosphorous compounds, such as methylene diphosphine dioxides and carbamoylmethylphosphine oxides and tetraoctyl-3-oxapentanediamide (TODGA) were used as neutral ligands in the polymeric sensor membranes. It was found that addition of certain substances that are called "anionic modifiers" in sensor terminology (tetra-bistrifluoromethylphenyl-borate (TFPB), chlorinated cobalt dicarbollide (CCD)) often results in increase of sensor sensitivity to lanthanides. Different sensors based on the extractants exhibit remarkable sensitivity to RE metal cations and their selectivity (cross-sensitivity) can be widely governed by changing the composition of the membranes. Chemical sensors based on the extractants show good promise for analysis of RE mixtures in complex solutions containing various other components. The developed sensors can be particularly interesting for the analysis of highly radioactive liquid waste (HLW).