In this present study, we have synthesized ferrous oxalate nanorods by a modified co-precipitation methods. The obtained nanomaterial (ferrous oxalate nanorod) was calcined at higher temperatures to form both maghemite and hematite nanorods. The morphology, size, crystalline phases, formation and surface area of the nanorods were characterized by scanning electron microscope, transmission electron microscope, X-ray diffraction, Fourier transform infrared spectroscope, ultraviolet–visible diffuse reflectance spectroscope and Brunauer–Emmett–Teller surface area analytical techniques. The results showed that high-yield aligned nanorods with a typical diameter of 100–200 nm and length up to micrometers were formed. The obtained rod-shaped nanomaterials (i.e., ferrous oxalate, maghemite and hematite) were used as adsorbents and were applied to remove Congo red (CR) dye molecules, which was used as a model of organic pollutants in aqueous solution. The adsorption isotherms and kinetics of removal of CR were studied. It was found that the adsorption capacity of maghemite nanorod is highest among the three adsorbents and can be regarded as an effective adsorbent for removal of CR from aqueous solution.