During last decades, some industrial processes (e.g., uranium, coal and phosphate mining, shale gas extraction) and nuclear accidents like Tchernobyl or Fukushima, have contributed to release radionuclides across the globe. Their persistence in the environment can contribute to ionizing radiations exposure risk to populations and ecosystems, and thus, environmental radiological monitoring is of great concern. Radium-226, alpha emitter whose progeny is the well-known radon gas, and Cesium-137, beta emitter, belong to the most radiotoxic radionuclides. Indeed, due to chemical properties respectively similar to those of calcium and potassium, they are able to replace them in biological processes, and can thus contribute to increase the internal dose. In order to assess the risk of chronic exposure, it is essential to have a deeper understanding of processes leading to radionuclides migration in the environment. However, their quantification in environmental samples (e.g., pore waters, root systems) presents many challenges: low sample volumes available (<10 mL), complex matrices and concentrations below instrumental detection limits. Their analysis requires the use of efficient sample pretreatment methods, combined to sensitive analytical methods. But existing sample pretreatment techniques fail to answer these criteria since they are multi-stage, time-consuming, often lack of selectivity and are not suitable for small sample volumes. This work aims to develop new sorbents showing high selectivity for these two radionuclides, in order to perform their determination with inductively coupled plasma mass spectrometry (ICP-MS), in small volumes of complex samples. In this context, synthesis of ion-imprinted polymers (IIPs) has for the first time been proposed in extraction and preconcentration processes of Ra and Cs. Several IIPs have been synthesized using non radioactive elements as template ions: Cesium (Cs-133) and Barium, as an analog of Ra. Different syntheses have been achieved, modifying either the nature of reagents, solvents or proportions, in order to study their influence on selectivity. Non-imprinted polymers (NIPs) were synthesized and used in parallel to control the presence of specific cavities on IIPs. For this, polymers were packed in cartridges to characterize them by solid phase extraction (SPE), by comparing extraction recoveries between IIPs and NIPs. A first optimization of the washing step highlighted a good selectivity of IIPs for their template ions, with recoveries from 12 to 30% higher than NIP. This selectivity was further confirmed in presence of interfering ions from different chemical classes, under various chemical forms depending on the conditions of use (such as pH) of the IIPs : Mg, Sr, Mo, W, In, Tl, Pb, Bi, Nd, Th and U.