Magnetic nanomaterials especially ferrites are gaining more interest recent years for environmental and biomedical applications. The preparation of non-stoichiometric zinc ferrite nanoparticles [(ZnxFe1-x)O•Fe2O3] was achieved by a modified co-precipitation route . The obtained samples were characterized by Scanning electron microscopy (SEM), X-ray diffraction (XRD), and Vibrating Sample Magnetometer (VSM). All samples have crystallite sizes in the range of 3-7 nm. The hysteresis curves for magnetic properties showed a very low coercivity tending to zero for pure ZnFe2O4. This behavior is attributed to the crystallite size which is smaller than that of a single domain. The prepared samples were evaluated upon removal of Alizarin yellow dye and various parameters for the adsorption process were studied. The adsorption process showed high removal efficiency, which reached to 93% in the case of the zinc ferrite sample with maximum zinc molar ratio. The removal efficiency was found to increase with increasing molar ratio of Zn. The obtained nanopowders were also tested for their antimicrobial activity against Gram-negative bacteria, Gram-positive bacteria, and pathogenic yeast. The sample with the highest molar ratio of zinc showed potent antimicrobial activity against Bacillus cereus, Staphylococcus aureus, and Candida albicans. The ZnFe2O4 sample is considered a promising antimicrobial agent.