Recently, there has been growing interest in the use of natural available materials to prepare superabsorbents due to their low-cost and environmental friendliness. In this study, a biodegradable organic–inorganic superabsorbent was prepared through graft copolymerization of acrylic acid (AA) onto xyloglucan (XG) polysaccharide chains, in the presence of diatomite as an inorganic material, N,N′-methylene-bis-acrylamide (MBA) as a cross-linker and ammonium persulfate (APS) as an initiator, in an aqueous solution (XG-g-PAA/diatomite). The synthesized hydrogel nanocomposite was characterized with FTIR, SEM, TGA and XRD. In this contribution, the properties such as swelling and water retention behavior of the XG-g-PAA/diatomite were investigated. Moreover, the influence of each starting material content on the water absorbency property of the XG-g-PAA/diatomite composite was systematically studied. The results showed that the composite water absorbency capacity was 1057.06 ± 69.53 g g⁻¹ in deionized water and 65.67 ± 5.43 g g⁻¹ in a 0.9 wt% NaCl saline solution under the optimized conditions. The excellent properties of the prepared SAP composite suggested that it could find a diverse range of applications such as in hygienic products, agriculture and waste-water treatment. Furthermore, being biodegradable and low-cost could be added advantages for the XG-g-PAA/diatomite superabsorbent composite.