A vehicle side door structure includes an inner panel, an outer panel that is positioned on the outside of the inner panel in the vehicle-width direction, and that forms a closed space in cooperation with the inner panel. In addition, an impact beam extends in the longitudinal direction of a vehicle body, and is arranged within the closed space at a position close to the outer panel, a bracket is attached to the inner panel and holds, at a portion which is on the inner side of the inner panel in the vehicle-width direction, a collision detector, and a load transmission member connects the impact beam to the inner panel at a portion that overlaps the bracket from a lateral view.