A new mesoporous adsorbent iPCalixC5X containing 1,3-alternate calix[4]crown-5 derivative iPCalixC5 was prepared by vacuum suction. It was immobilized into the pores and channels of XAD-7, a polar carrier containing polyalkyl ester, by introduction and self-assembly. The uptake of Rb, Cs, K, and a total of 20 coexisting metals onto iPCalixC5X was investigated in the range of 0.4-6.0 M HNO3. The separation factor (SF) of Rb with Cs was 186.5 in 1.0 M HNO3 and 95.83 in 3.0 M HNO3. The Rb adsorption capacity was 0.5239 mM/g under the conditions of 298 K, 3.0 M HNO3, and a contact time of 120 min. The removal efficiency was greater than 99.6% for Rb and less than 0.22% for Cs. The Rb adsorption data fitted well with the Langmuir model, reflecting the monolayer adsorption mechanism. The thermodynamic parameters Delta H degrees, Delta G degrees, Delta S degrees, and some fundamental chemical engineering data of Rb adsorption were obtained. Efficient Rb removal from Cs-containing effluents by iPCalixC5X is promising.