The preparation and characterization of a novel type of castor oil-based polymer inclusion membrane (PIM) was investigated, focusing on its flux and selective recovery of Ca2+ over competitive ions such as K+, Na+, and Mg2+. The PIM contains a cross-linked high-molecular-weight green polyol (GPO) as a polymer base, benzene-18- crown-6 as a carrier, and an ionic liquid called 1-Butyl-3-methylimidazolium chloride as a plasticizer. GPO was first synthesized by a reaction between an epoxidized castor oil and a cellulose acetate, thereafter, cross-linked by isophorene isocyanate. The base polymer and the prepared PIM were characterized by gel permeation chromatography (GPC), Fourier transform infrared spectroscopy (FTIR), scanning electron microscope (SEM), atomic force microscopy (AFM), thermogravimetric analysis (TGA), and X-ray diffraction (XRD). The FTIR results indicate that oxirane groups in the epoxidized castor oil molecules reacted with the primary hydroxyl groups of cellulose acetate chains. The contact angle measurement hints at the hydrophobic characteristics of the prepared membrane. Compared to the PVC-, CA-, and PVDF-based polymer inclusion membrane, the cured GPO-based PIM, showed higher selectivity and flux of calcium ions with thesame composition. The greater stability and significantly higher surface roughness are further favorable features of the novel PIM.