Solid particles are essential for stabilising Pickering emulsions and improving interfacial catalytic reactions. We constructed magnetic polydopamine nanoparticles to stabilise lipase-Pickering emulsions for olive oil deacidification. The results showed that the nanoparticles had a core-shell structure with an average particle size of 605.8 nm, a zeta potential of -39.3 mV and a contact angle of 55.9°, which effectively stabilised the emulsion. The particles were added to the lipase solution and sonicated to construct the emulsion system. The emulsion droplets were the smallest and most uniformly distributed under 400 W ultrasonic irradiation for 10 min. The lipase adsorbed on the oil-water interface and promoted the hydrolysis of olive oil. The released fatty acid content increased 1.7-fold compared with the non-emulsion. This study not only provides a new immobilisation method for the interfacial catalysis of lipase but also provides ideas for the high-value utilisation of high acid-value oil resources.