Polyacrylamide/sodium alginate modified montmorillonite (PAM/SA-MMT) superabsorbent composites were synthesized by free-radical polymerization under normal atmospheric conditions. They were characterized by X-ray diffraction, scanning electron microscopy, and Fourier transform infrared spectroscopy (FTIR). Their water absorbency and methylene blue (MB) adsorption behaviors were studied. Compared with PAM/MMT composites, PAM/SA-MMT composites demonstrated greater water absorbency (863 g g−1 in distilled water and 101 g g−1 in 0.9 wt % NaCl solution) and higher adsorption capacity of 2639 mg g−1 for MB. The adsorption behaviors of the composites showed that the isotherms and adsorption kinetics were in good agreement with the Langmuir equation and pseudo-second-order equation, respectively. FTIR analysis suggested that the MB adsorption of PAM/SA-MMT composites via a mechanism combined electrostatic, H-bonding and hydrophobic interaction. © 2013 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2014, 131, 40013.