This work was carried out to investigate the effect of HA nanoparticle shape on the biodegradation behaviour of a magnesium-hydroxyapatite (Mg-2Zn-0.2Mn-0.5Ca/1HA, wt%) nanocomposite fabricated by a novel route which combines high shear solidification (HSS) and equal channel angular extrusion (ECAE) techniques. Two common shapes of HA nanoparticles, i.e. spherical and needle-like were selected with an average equivalent diameter of 40 nm. The biodegradation rate of the nanocomposite in HBSS Hanks’ Balanced Salt Solution was assessed using electrochemical corrosion and immersion test. Scanning electron microscopy (SEM) and energy dispersive spectroscopy (EDS) were used to characterize the surface microstructure, biodegradation morphology and biodegradation products. Experimental results showed that Mg/HA composite with spherical HA nanoparticles exhibited a significantly smaller biodegradation rate of 0.6 ± 0.05 mm/year, compared to 9.41 ± 2.53 mm/year for the nanocomposite with needle HA nanoparticles.