A vehicle side door structure is provided including: an outer panel that configures a portion at a vehicle width direction outer side of a side door and that extends along a vehicle up-down direction and a vehicle front-rear direction; an inner panel that configures a portion at a vehicle width direction inner side of the side door, that extends along the vehicle up-down direction and the vehicle front-rear direction, and that, together with the outer panel, forms an internal space; an impact beam having both length direction end portions fixed to the inner panel, that is configured in a straight tube shape extending along the vehicle front-rear direction, and that is disposed at an outer panel side in the internal space; and a sensing bracket that is provided at the impact beam and that juts out from the impact beam toward the outer panel.