South Dakota Highway 48 (SD 48) is a 12.462-mile (20.056 km) state highway in Union County, South Dakota, United States, that begins at Interstate 29, about 2.5 miles (4.0 km) west of Spink, and becomes Big Sioux River Road, formerly Iowa Highway 403, northwest of Akron, Iowa.

SD 48 begins at a diamond interchange on I‑29 Exit 31, approximately 44 miles (71 km) south of Sioux Falls. From its western terminus, SD 48 travels due east. It nearly immediately meets County Road 1C (CR 1C), an old alignment of US 77. Two miles (3.2 km) east of the CR 1C intersection, SD 48 passes through the town of Spink.

East of Spink, SD 48 gently curves to the north as it descends a rolling hill towards Brule Creek. After crossing the stream, the highway ascends, bending back to the south to resume its due east course. Over the next several miles, the road remains arrow-straight while traversing gently rolling farmland. Just under 10 miles (16 km) east of I‑29, SD 48 serves as the southern terminus of Highway 11 (SD 11). About 1⁄3 mile (0.54 km) from the SD 11 junction, SD 48 crosses a bridge over West Union Creek; one mile (1.6 km) later, it crosses East Union Creek. For the remainder of the route, the road gradually S-curves southwest into the Big Sioux River valley. At the Big Sioux River, the road crosses the Iowa state line and ends.

South Dakota 48 was established on a previously unnumbered highway between 1948 and 1953. It began at U.S. Highway 77 (current Union County Road 1C). No significant changes have been made, except for a slight extension to meet Interstate 29 to the west, and a slight realignment at the Iowa border.

The entire route is in Union County.

Location	mi	km	Destinations	Notes
​	0.000	0.000	I-29	I-29 exit 31
​	9.891	15.918	SD 11
Big Sioux River	12.462	20.056	South Dakota–Iowa state line
			Big Sioux River Road to Iowa 12	Continuation into Iowa
1.000 mi = 1.609 km; 1.000 km = 0.621 mi

• List of state highways in South Dakota

Media related to South Dakota Highway 48 at Wikimedia Commons