This paper focuses on the structural characteristics of membranes used in the removal of benzene from a dilute aqueous solution of benzene by pervaporation. Poly(methyl methacrylate)-graft-poly(dimethylsiloxane) (PMMA-g-PDMS) and poly(methyl methacrylate)-block-poly(dimethylsiloxane) (PMMA-b-PDMS) membranes containing tert-butylcalix[4]arene (CA), (CA/PMMA-g-PDMS and CA/ PMMA-b-PDMS) were studied. When an aqueous solution of 0.05 wt % benzene was permeated through CA/PMMA-g-PDMS and CA/PMMA-b-PDMS membranes, these membranes showed strong benzene permselectivity. Both the permeability and the benzene permselectivity of CA/PMAM-g-PDMS and CA/ PMMA-b-PDMS membranes were enhanced by increasing the CA content, due to the affinity of the CA for benzene. The permeability and the benzene permselectivity of CA/PMMA-b-PDMS membranes were much greater than those of CA/PMMA-g-PDMS membranes. Transmission electron microscope (TEM) observations revealed that both the CA/PMMA-g-PDMS and CA/PMMA-b-PDMS membranes had a microphase-separated structure consisting of a PMMA phase and a PDMS phase-containing CA. The microphase-separated structure of the latter membranes was much clearer than that of the former and was larnellar. The distribution of CA in the microphase-separated structure of the CA/PMMA-g-PDMS and CA/PMMA-b-PDMS membranes was analyzed by differential scanning calorimetry.