In this study, chitosan (CS), Na+-bentonite (Na+-BNT) and chitosan/organo-bentonite (CS/O-BNT) biodegradable composites having three different compositions were investigated. Electrokinetic measurements were examined in aqueous medium by taking the effects pH, electrolytes (NaCI and BaCl2), surfactants (CMB and SDS), and temperature into account. It was noticed that the initial zeta-potential of Na+-BNT shifted from negative (zeta = -35 mV) to positive region (zeta = +13 mV) with increasing polycationic CS content in the composite structure as aimed. Divalent 2:1 electrolyte (BaCl2) caused to shift the zeta potentials of all the dispersions to more positive regions. While the most negative effect on zeta-potential of the composites was reached with SDS, which reduced the value of zeta-potential to -39 mV for CS(1)10-BNT composite, the most positive effect was monitored with CTAB (zeta= +40 mV) for CS(3)/O-BNT composite. Further, the composites were tested against various bacterial (Gram-positive and Gram-negative) and fungal microorganisms at various concentrations and results obtained were compared with the reference antibiotics and fungicide. According to inhibition zone values accomplished, antibacterial and antifungal activities of the CS/O-BNT composites are increased with increasing CS content as proportional with their positive zeta-potential values. (C) 2017 Elsevier Ltd. All rights reserved.