IIn the present study, modified carboxymethyl cellulose (CMC) was prepared to form nano phosphonate carboxy methyl cellulose (PCMC) for removal of cationic dyes Crystal violet (CV) and Methylene blue (MB) as models. The produced nanostructure and morphology of the adsorbent PCMC were investigated by (FTIR) Fourier transform infrared spectroscopic analyses, transmission electron microscopy (TEM), zeta potential test, and scanning electron microscopy (SEM). The spectrophotometric characterization of nano adsorbent surface PCMC was studied for the removal of both cationic dyes as a function of adsorption contact time, initial concentration of solution, amount of nano adsorbent, adsorption temperature, and solution pH value. The equilibrium adsorption data of both MB and CV dyes agreed well with the Langmuir model (R2 = 0.9942 and 0.9958 for dyes, respectively), which indicates the maximum adsorption capacity of the PCMC nanoparticle-based adsorbent for both dyes. The kinetics of adsorption process fit a pseudo-first-order model. The adsorption process is spontaneous and endothermic, as determined by investigations of thermodynamic characteristics within the temperature range (298–313 K). Based on the adjusted parameter, the adsorbent exhibits very high removal efficiency and speed for both dyes.