Mg-Gd alloys show a good combination of mechanical properties and corrosion rates. This has led to the interest in developing Mg-Gd based alloys for medical applications as implant materials. The deformation behaviour of Mg-Gd alloys subjected to fatigue was investigated previously and in extruded alloys the failure occurs in a ductile manner. The role of the intermetallic particles in twinning deformation on the propagation of cracks that form during fatigue deformation remains unclear. In the present study the microstructure of the fatigue tested samples are investigated with optical and scanning electron microscopy (SEM) equipped with EBSD to determine the role of twinning and orientation of the grains on the propagation of fatigue cracks. A significant increase in the amount of twins near the fracture surface was detected with majority being tension twins. The relationship between the propagation of fatigue cracks and role of twins will be discussed.