A sun gear for a mechanical reduction gear of a turbine engine, in particular for aircraft, the sun gear having a general annular shape about an axis and comprising at the outer periphery thereof, a meshing gearing with planet gears of the reduction gear, and at the inner periphery thereof, splines for coupling with an input shaft of the reduction gear, characterised in that the sun gear has a staged profile in axial cross-section, and preferably comprises an annular recess opening radially inwards and configured to receive at least one oil jet.