Abstract Emulsion templating of high internal phase emulsions (HIPEs) was used to synthesise microcellular poly(styrene-co-divinylbenzene) magnetic nanoparticle composites with open, interconnected, porous structures. The emulsions were stabilised by a combination of a surfactant and maghemite/magnetite (uncoated or coated with oleic acid) nanoparticles and then cured thermally. Up to 23 wt% (with regards to complete composite mass) of magnetic nanoparticles were incorporated into the polymer matrix. Composite polymers exhibited magnetic properties with a saturation magnetisation of 13 emu/g and a substantial heating effect at the AC magnetic field of 3.8 kA/m and a frequency of 104 kHz. A nanocomposite polyHIPE sample with coated nanoparticles exhibited a higher hyperthermia effect. Samples retained typical polyHIPE morphology with cavity diameters of approx. 8 μm and interconnecting pores of around 0.8 μm in diameter. Compared to styrene/divinylbenzene polyHIPEs without nanoparticles, the openness (interconnecting pore size to cavity size ratio) was slightly reduced. Materials were characterised with gas adsorption porosimetry, XRD, TGA/DSC, SEM, TEM.