In this study, polymeric nanoparticles were used as an adsorbent to remove the textile dye Direct Blue 9 (DB9) from an aqueous solution. Adsorption capacity of the polymeric nanoparticles were determined in various conditions such as pH, temperature, and dye concentration. Kinetic parameters were also calculated. Optimum initial pH, temperature and equilibrium time were determined as 6.0, 318 K and 90 minutes, respectively. The maximum adsorption capacity of adsorbent and percentage removal of DB9 were detected as 15.49 mg/g and 98.15%, respectively. To clarify the nature of the adsorption process isotherm, thermodynamic and kinetic studies were also performed. The adsorption process obeys the Langmuir isotherm model and pseudo-second order model.