State Route 300 (abbreviated SR 300) is a four-lane controlled-access expressway inside of Memphis, Tennessee that goes from Interstate 40 to U.S. Highway 51.

The route that is now SR 300 was originally envisioned as a freeway known as the Mud Island Expressway, which would have extended from the present-day eastern terminus across Mud Island to I-40 near downtown.

SR 300 was originally part of an abortive effort in the 1960s to build an expressway connecting the northern portion of the then Interstate 240 to Mud Island.

Ghost ramps and abandoned grading for this expressway still exist at the current western terminus of SR 300 at U.S. Highway 51 and also at Interstate 40 Exit 1 in downtown Memphis.

In November 2004, the Tennessee Department of Transportation announced alternative A-1 (SIU 9) as the preferred alignment of future Interstate 69 through the Memphis area which will include SR 300.