A sunshade assembly includes a winding shaft, a sunshade curtain wound around the winding shaft, a pull rod connected to the sunshade curtain end distal from the winding shaft, and two guide rail units. Each guide rail unit includes a longitudinal rack member in a direction transverse to the winding shaft. A link unit includes a connecting shaft and two pinion gears respectively attached to the connecting shaft and meshed with the rack members. A resistance unit includes a base mounted to the pull rod and frictionally contacting the connecting shaft to provide a resisting force against rotation of the connecting shaft.