The boat trailer tug includes a primary frame with a mounting beam that is attachable to a boat trailer frame. A primary collar is fixed to the mounting beam front end. A hitch tongue is connected to the collar and extends forward from the collar. A hitch ball receiver is mounted on a front end of the hitch tongue for connecting the tug to a towing vehicle. A vertical height adjustment frame is slidably connected to the collar. A linear actuator moves the height adjustment frame up and down relative to the collar. A power unit frame is pivotally attached to the height adjustment frame for pivotal movement about a vertical axis. A motor, transmission and driven wheels are mounted on the power unit frame. The linear actuator raises and lowers the driven wheels. A steering system pivots the power unit frame to steer the tug.