Majorite garnets with the composition Mj70Py30 have been deformed in the multi-anvil apparatus at 17 GPa and 2000 °C. The microstructure has been characterized by transmission electron microscopy. It is shown that under these conditions majorite garnet is ductile. Dislocations with <100> and ½<111> Burgers vectors are observed with a density 1–5 × 1012 m−2. The absence of clear glide planes and the occurrence of subgrain boundaries suggest the importance of diffusion and climb in the plasticity of majorite garnets in mantle transition zone conditions.