We developed a novel hyperthermia material for cancer therapy, cationic albumin-conjugated magnetite nanoparticles (MNPs), which absorb the energy of an alternating magnetic field and convert it into heat. MNPs of about 10 nm were synthesised through co-precipitation, and citric acid was used to stabilise the MNP suspension. Then albumin was cationised by replacing anionic side chain groups with cationic groups. The surface modification of the MNPs was provided by cationic albumin, which was covalently conjugated to carboxylic acid functions located at the distal end of the MNPs' surface by carbodiimide chemistry. Finally, we obtained stable superparamagnetic suspensions with particle sizes of 140 nm and saturation magnetisation of 67 emu/g, which do not have the disadvantage of eventual desorption of physical attachment. We also analysed the potential of these particles for magnetic fluid hyperthermia by determination of the specific absorption rate at a constant frequency of 215 kHz; the temperature increase of the particles was 30.8 °C. This study experimentally demonstrates the high efficiency of these nano-heaters.