Flame-retardant and super paramagnetic zinc ferrite (ZF) was adopted to decorate boron nitride nanosheet (BNNS) through a typical solvothermal method so as to afford ZF-BNNS nanofiller with improved flame-retardant performance. The resultant ZF-BNNS nanofiller was filled in epoxy resin (EP) and exposed to a weak magnetic field (0.05 T) in order to achieve ordered orientation in the EP matrix and improve the flame-retardant performance of EP-matrix composites. Results show that the weak magnetic field accommodates the ordered alignment of ZF-BNNS nanofiller in EP matrix, and the well-ordered ZF-BNNS nanofiller is superior to the randomly distributed one in enhancing the fire resistance of EP. Namely, the well-ordered ZF-BNNS nanofiller is able to reduce the peak heat release rate, peak smoke production release and CO production of EP-matrix nanocomposite by 48.5%, 46.0%, and 66.6%, respectively. This is because the ZF-BNNS nanofiller can increase the char yield of EP at elevated temperatures while layered-ordered BNNS and ZF exhibit synergistic flame-retardant effect: the well-aligned BNNS may act as a strong physical barrier to retard the release and diffusion of thermally decomposed products via the so-called "tortuous path" effect, and ZF may act as the catalyst to promote the carbonization and char layer formation. As a result, the density and strength of the carbon layers are increased in association with enhanced insulation shield effect to heat flux, oxygen and combustible pyrolysis products as well as their suppressed release and transfer during combustion. Moreover, ZF-BNNS/EP nanocomposites exhibit higher tensile strength and storage modulus than pure EP and BNNS/EP, which is due to the incorporation of ZF-BNNS nanofiller with good dispersion in EP matrix.