Fe3O4@HA@Ag magnetic nanocomposites (MNCs) were successfully synthesized by the simple reflux method for the removal of azo dyes from the industrial aqueous media. Fe3O4@HA@AgMNCs exhibited high catalytic activity to reduce MB within 20min from the waste water. The obtained materials were characterized by the means of different techniques. Powder X-ray diffraction (XRD) analysis confirmed the single-phase of Fe3O4 spinel structure. SEM and TEM analysis indicated that Fe3O4@HA@AgMNCs were nanoparticles like structure with small agglomeration. TG result showed that the products contained 9% of HA. The characteristic peaks of HA at 1601cm−1 and 1703cm−1 was observed by the means of FT-IR spectra of Fe3O4@HA@AgMNCs. The hysteresis (σ–H) curves revealed Fe3O4@HA@Ag MNCs exhibit a typical superparamagnetic characteristic with a saturation magnetization of 59.11emu/g and measured magnetic moment is 2.45µB. The average magnetic particle dimension (Dmag) is 13.25nm. In accordance, the average crystallite and particle dimensions were obtained as 11.50nm and 13.10nm from XRD and TEM measurements, respectively. Magnetocrystalline anisotropy was offered as uniaxial and calculated effective anisotropy constant (Keff) is 2.96×105Erg/g. The blocking temperature was estimated as 522K. The size-dependent saturation magnetization suggests the existence of a magnetically dead layer as 0.793nm for Fe3O4@HA@Ag MNCs. The UV–vis diffuse reflectance spectroscopy (DRS) and Kubelka–Munk theory were applied to determine the optical properties of powder samples. The direct optical energy band gap (Eg) values were estimated from Tauc plots between 1.62eV and 2.12eV. An illustration for the fabrication of Fe3O4@HA@Ag MNCs. Display omitted •The reduction of azo dye such Methylene Blue was instantly completed with Fe3O4@HA@Ag MRCs.•Fe3O4@HA@Ag MRCs was used as heterogeneous catalyst.•Fe3O4@HA@Ag MRCs with the room-temperature magnetism showed that it could be used as a recyclable catalyst.•The direct Eg value of Fe3O4 NPs exhibits a remarkable increase from 1.62eV to 2.12eV after the HA coating.