In this study effect of acidity on polymer/clay nanocomposites was investigated. Bionanocomposites (X-MMT) were obtained using hemicellulosic polysaccharide from corn cob (xylan), and sodium activated smectite-type clay (montmorillonite, NaMMT) in acidic (pH 4), neutral (pH 7), and basic (pH 10) media. Acidity of media was adjusted using identical amounts of appropriate buffer solution in dispersion preparation process. X-MMT dispersions showed a steady zeta potential about -12 mV, regardless of medium pH. NaMMT dispersions did not obey to Bingham's model giving negative yield values. But X-MMT samples showed Bingham plastic behavior mostly. Intercalation by xylan was determined as an expansion in basal spacing (d(001)) of NaMMT about 1.67 +/- 0.05 nm for all pH values. Structural hydroxyl stretching band at 3625 cm(-1) disappeared for X-MMT samples, which was a strong evidence of xylan-NaMMT interaction. Rheological and electrokinetic behaviors of X-MMT bionanocomposite dispersions were strongly influenced from the medium acidity, whereas intercalation of clay was identical for all pH values. (c) 2012 Elsevier B.V. All rights reserved.