This paper demonstrates the application of negative charge-functionalized carbon-encapsulated superparamagnetic colloidal nanoparticles being as nanoadsorbents for the removal of cationic dyes from aqueous solutions. Adsorption characteristics of the magnetic nanoadsorbents were examined using methylene blue as adsorbates, exhibiting excellent ability to remove cationic dyes from aqueous solutions. In addition, the influences of uptake time, concentration of nanoadsorbents and pH values of aqueous solution on the removal of cationic dyes have been discussed. Results show that the removal efficiency can be up to 90% at a dye concentration of 100 mg L-1 when the uptake time is 1 min, which indicates rapidly removal ability of the magnetic nanoadsorbents. Furthermore, other cationic dyes including rhodamine B and methyl violet were used to examine the universality of nanoadsorbents.