The adsorption of crystal violet from an aqueous solution by polyacrylic acid-bound magnetic nanoparticles was studied. It was shown that the magnetic nano-adsorbent was quite efficient or the adsorption/desorption of crystal violet. In the aqueous solution of crystal violet at 25degreesC, the adsorption behavior followed the Langmuir adsorption isotherm with a maximum adsorption amount of 116 mg g(-1) and a Langmuir adsorption equilibrium constant of 0.005 L mg(-1). In the methanol solution of acetic acid (1.0-8.0%), desorption of crystal violet increased up to 100% with increasing the acetic acid concentration. The reusability of magnetic nano-adsorbent and the effects of temperature, pH, and phosphate on the adsorption of crystal violet were also investigated. Additionally, it was very noteworthy that the adsorption/desorption rate of crystal violet was quite fast (required time < 1 min) clue to the absence of pore-diffusion resistance. The developed magnetic nano-adsorbent will be useful in the removal of cationic dyes from wastewater.