In this present study, a facile and green method to synthesize highly stable FeO-guar gum nanocomposite using ultrasound was reported. Thermal gravimetric analysis, fourier transform infrared spectroscopy, X-ray diffractometry, field emission scanning electron microscopy, energy dispersive spectroscopy, high resolution transmission electron microscopy and X-ray photoelectron spectroscopy were used to characterize the crystal structure, size and morphology, elemental composition, metal-metal and metal-oxygen bonds of the synthesized nanocomposites. FeO-guar gum nanocomposite with a size of ∼48nm was obtained as from TEM. The physicochemical characterization supports the feasibility of guar gum as an efficient stabilizing agent for the formation of nanocomposite; guar gum acts as a capping agent with a zeta potential value of -34.8 which was found to be beneficial for achieving lower particle size. Guar gum serves as a matrix for both reduction and stabilization of nanocomposite. The HR-TEM and XPS shows that FeO nanoparticles are encapsulated by the guar gum polymeric networks or FeO-guar gum core-shell structure. The guar gum encapsulated magnetite nanocomposite has performed better in terms of catalytic activity for the liquid phase reduction of p-nitroaniline. The simple catalytic reduction of p-nitroaniline showed an efficiency of 47% and further exceptional improvement of up to 98% reduction within 60min with the addition of sodium borohydride was achieved. The sonochemical synthesis of FeO-guar gum nanocomposite does not require stringent experimental conditions or any toxic agents, and thus, a straightforward, rapid, efficient and green method for the fabrication of highly active catalysts for treating environmental pollutants.