Nanocomposites play a key role in the removal of toxic metal(loid)s from environmental water. In this study, we investigated the adsorption capability of water-soluble carboxymethyl chitosan (WSCC)-modified functionally oxidized single walled carbon nanotubes (oSWCNTs) for rapid and efficient removal of toxic Pb(II) from water. The WSCC–oSWCNTs nanocomposite was prepared by an acid treatment of SWCNTs followed by an ultrasonic dispersion process using WSCC as dispersant. The morphology and chemical characteristics of the WSCC–oSWCNTs nanocomposite were further identified using various characterization techniques (i.e., transmission electron microscopy, TEM; scanning electron microscopy, SEM; Raman spectra; Fourier transform infrared spectroscopy, FTIR; X-ray photoelectron spectroscopy, XPS; nitrogen adsorption–desorption isotherm test). The efficiency of the adsorption process in batch experiments was investigated via determining various factor effects (i.e. WSCC–oSWCNTs nanocomposite concentration, solution pH, initial Pb(II) concentration, contact time, and reaction temperature). Kinetic results showed that the adsorption process followed a pseudo-second-order, while an isotherm results study showed that the adsorption process followed the Langmuir and Freundlich isotherm models at the same time. In addition, the van't Hoff equation was used to calculate thermodynamic parameters for assessing the endothermic properties and spontaneity of the adsorption process. The WSCC–oSWCNTs nanocomposite manifested a high adsorption capacity for Pb(II) (113.63 mg g⁻¹) via electrostatic interactions and ion-exchange, as its adsorption rate could reach up to 98.72%. This study, therefore, provides a novel adsorbent for the removal and detection of harmful residues (i.e. toxic metal(loid)s) from environmental water, such as industry wastewater treatment and chemical waste management.