A series of novel superabsorbent nanocomposites were prepared by the solution radical polymerization of natural guar gum (GG), partially neutralized acrylic acid [sodium acrylate (NaA)], and cation-exchanged vermiculite (Mn+-VMT) with ammonium persulfate as the initiator in the presence of the crosslinking agent N,N'-methylene-bis-acrylamide. Fourier transform infrared analysis revealed that NaA was grafted onto the GG chains and that Mn+-VMT participated in the polymerization. X-ray diffraction results showed that the occurrence of the cation-exchange process changed the interlayer gap of vermiculite (VMT) and that Mn+-VMT was exfoliated during polymerization to form a nanocomposite. The exfoliated VMT led to better dispersion in the GG-g-poly(sodium acrylate) matrix, as shown by scanning electron microscopy and transmission electron microscopy analysis. Mn+-VMT improved the water absorption of the nanocomposite more remarkably than raw VMT, and Al3+-VMT enhanced the water absorption to the highest degree. The nanocomposite exhibited intriguing overshooting swelling characteristics in a multivalent saline solution and acidic pH solution and showed switching pH-responsive behaviors in buffer solutions between pH 2 and pH 7.2. (C) 2010 Wiley Periodicals, Inc. J Appl Polym Sci 119: 3675-3686, 2011