A series of biopolymer chitosan/montmorillonite nanocomposites were prepared by controlling the molar ratio of chitosan and montmorillonite. The nanocomposites were characterized by UV, FTIR, XRD, SEM, TGA, and FL analysis were performed to confirm the observed results. Batch adsorption experiments were carried out utilizing the composite to adsorb Congo red from aqueous solutions. As a result, increasing adsorbent dosage and initial dye concentration along with decreasing agitation speed, temperature, and initial pH led to increasing the amount of adsorbed Congo red. A rapid increment in the adsorption was happened with increasing adsorbent dosage from (1.0, 2.0 and 3.0g/L), pH (3.4, 5.8 and 9.4) and temperature (30ºC, 45ºC, and 60ºC) while further increment in the adsorbent dosage resulted in an insignificant increase in the adsorption (22.0, 24.0, 29.0,mg g−1). The adsorption isotherms were also studied. It was shown that all the sorption processes were better fitted by the Langmuir and Freundlich isotherm equation. Moreover, the adsorption isotherm models were employed for the description of the Chitosan with montmorillonite nanocomposites dye adsorption processes. The antibacterial activity of Chitosan with montmorillonite nanocomposites showed more than 99% mortality against two Gram-negative bacteria and two Gram-positive bacteria. Because chitosan/montmorillonite nanocomposites could be recovered conveniently and possessed of excellent adsorptive property, it can be developed as an economical and alternative adsorbent to decolorize or treat dye wastewater.