The viscosity of CaMgSi 2 O 6 (diopside) liquid has been determined up to 13GPa and 2200 o C using in situ falling sphere viscometry with X-ray radiography. The experiments were carried out in a 1500t multianvil apparatus at the SPring-8 synchrotron (Japan). A new, high-pressure sample assembly was developed with LaCrO 3 replacing the traditionally used graphite furnace material, allowing experiments within the diamond stability field to be carried out. The viscosity of CaMgSi 2 O 6 liquid increases slightly from 3.5 to 10GPa and then decreases slightly at higher pressures. However, over the entire ranges of temperature (2030-2473K) and pressure (3.5-13GPa) investigated, variation in viscosity does not exceed +/-0.5log units. The viscosity results from this study are consistent with those calculated from the pressure dependence of oxygen self-diffusion in CaMgSi 2 O 6 liquid using the Eyring equation with a translation distance (λ) of 0.45nm providing the best correlation. Both sets of results indicate a change in pressure dependence at approximately 10GPa, where viscosity results show a maximum with pressure and silicon and oxygen self-diffusivity results show a minimum.