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Nanostructured ZnFe2O4 was synthesized by the heat treatment of a mechanically activated mixture of ZnO/α-Fe2O3. X-ray diffrac-tion (XRD) and differential thermal analysis (DTA) results demonstrated that, after 5 h of the mechanical activation of the mixture, ZnFe2O4 was formed by heat treatment at 750℃ for 2 h. To improve the characteristics of ZnFe2O4 for adsorption applications, the chemical activation process was performed. The 2 h chemical activation with 1 mol·L?1 HNO3 and co-precipitation of 52%?57% dissolved ZnFe2O4 led to an in-crease in the saturated magnetization from 2.0 to 7.5 emu·g?1 and in the specific surface area from 5 to 198 m2·g?1. In addition, the observed particle size reduction of chemically activated ZnFe2O4 in field emission scanning electron microscopy (FESEM) micrographs was in agree-ment with the specific surface area increase. These improvements in ZnFe2O4 characteristics considerably affected the adsorption performance of this adsorbent. Adsorption results revealed that mechano-thermally synthesized ZnFe2O4 had the maximum arsenic adsorption of 38% with the adsorption capacity of 0.995 mg·g?1 in a 130 mg·L?1 solution of As(V) after 30 min of agitation. However, chemically activated ZnFe2O4 showed the maximum arsenic adsorption of approximately 99% with the adsorption capacity of 21.460 mg·g?1 under the same conditions. These results showed that the weak adsorption performance of mechano-thermally synthesized ZnFe2O4 was improved by the chemical activa-tion process.