Iron oxide/carbon nanocomposites having a mass ratio of 1:5 were prepared using the simple, versatile and environmentally friendly combustion synthesis method. The effect of experimental conditions, such as the fuel nature (urea, citric acid), reaction atmosphere (air, controlled atmosphere) and the time span of thermal treatment (30 and 60 min) on the nanocomposites characteristics were studied. Using citric acid as fuel, in the absence of air, maghemite or magnetite can be obtained by extending the time span of thermal treatment from 30 to 60 min. The adsorption capacity of the magnetite/carbon nanocomposite was investigated for the removal of two anionic (Acid Orange 7 and Acid Blue 129) and two cationic (Methylene Blue and Rhodamine 6G) dyes from simulated wastewaters. The effect of different parameters such as solution pH, adsorbent dose and contact time on the adsorption process was evaluated. The adsorption mechanism is controlled by electrostatic forces and is highly dependent on the pH. The removal efficiency of anionic dyes decreases while of cationic dyes increases with the increase of the pH value. The adsorption kinetics of the four dyes was described by the pseudo-second order model and the equilibrium data were correlated by the Langmuir isotherm. The capacity of regeneration and reuse of the adsorbent was evaluated in five cycles of adsorption-desorption. The combination of high adsorption capacity, excellent separation capability, short equilibrium time and high stability, indicates that the as-prepared magnetite/carbon nanocomposite is an excellent adsorbent material for the removal of both anionic and cationic dyes from wastewaters.