The largest amounts of Lanthanides are used in catalysis. Some of the rare earth elements are used in the glass and ceramic industries, metallurgy, electronics and even in water treatment and biomedicine. The fluorescent properties of the Lanthanide compounds are of special interest. The immobilization of cations on polymers with selective sorption properties allows the use of lanthanide compounds in processes where separation of the phases is required. Anion exchangers containing electron donating atoms (amines, hydroxyl groups) retain lanthanide cations as a result of complex formation reactions. It is known that polymers containing quaternary ammonium nitrogen can adsorb lanthanides only in the form of anionic complexes. These polymers do not contain electrondonating atoms in their matrix and therefore, theoretically, cannot interact with metal ions. However, our previous investigation shows that such kind of polymers, in certain conditions, are able to interact with cations in M2(SO4)3 solutions, where M is Fe3+, Cr3+, Ga3+, In3+or Al3+. In this communication the results of investigation on the influence of pH and temperature on Lanthanides(III) cations sorption on Purolite A-400, a polymer containing ammonium quaternary nitrogenare presented. The results of the study of the sorption kinetics of La3+, Nd3+, Eu3+ and Er3+ at 21 and 50^oC are also presented. It is shown that sorption of Lanthanide(III) cations on the Purolite A-400 polymer increases slightly with increasing temperature. Both at 21°C and 50°C with the pH increase of the solution, the sorption of the Lanthanide(III) cations increases significantly. The kinetic curves obtained experimentally were calculated with pseudofirst order (PFO) and pseudo-second-order (PSO) kinetic models.The kinetic curves, calculated with the PSO model, are close to those obtained experimentally, which confirms that this model adequately describes the kinetics of sorption of Lanthanide(III) cations on the Purolite A-400. The non-linear dependence of -ln(1-F) = f(t) shows that the sorption rate of cations containing Lanthanides(III) on Purolite A-400 at both 21 so and at 50^oC is limited by the internal diffusion. The linear dependence S = f (t0.5) also confirms that the internal diffusion is the rate limiting step of sorption of lanthanide cations both at 21°C and at 50^oC.