In this study, a new epoxy-triazinetrione (ETT)-functionalized magnetic nanoadsorbent (Fe3O4-ETT) has been developed for the removal of malachite green (MG) and Pb­(II) from aqueous solutions. Fe3O4-ETT as a nano-adsorbent was successfully synthesized through chemical modification of Fe3O4 nanoparticles with ETT. Characterization of Fe3O4-ETT nanoparticles using Fourier transform infrared, field emission scanning electron microscopy, transmission electron microscopy, energy-dispersive X-ray, X-ray diffraction, thermogravimetric analysis, vibrating sample magnetometer, and Brunauer–Emmett–Teller (BET) analyses revealed that the Fe3O4 nanoparticles were effectively modified with ETT. Numerous amine and hydroxyl groups of the triazine ring on the nano-Fe3O4 particles were mainly responsible for the adsorption of cationic organic dye and heavy metals through multiple interactions. Based on the BET analysis, an improved surface area from 42,000 to 84,788 m2 kg–1 was achieved after the surface modification of Fe3O4 NPs by ETT. The adsorption isotherm experiments revealed that the adsorption processes of MG and Pb­(II) were better described via applying the Freundlich isotherm model. Moreover, the kinetic pseudo-second-order model better described the adsorption data. The results also showed that the MG and Pb­(II) pollutants could be adsorbed by the Fe3O4-ETT through two different adsorption mechanisms, including electrostatic interactions and surface complexation, respectively. In addition, the magnetic nano-adsorbent can be regenerated and reused for MG and Pb­(II) removal from waters in several adsorption cycles. Thus, the excellent regeneration, low cost, and an easy synthesis route make Fe3O4-ETT an efficient nano-adsorbent for purification of water and wastewater contaminated by organic and inorganic pollutants.