Minnesota State Highway 139 (MN 139) is a 3.913-mile-long (6.297 km) highway in southeast Minnesota, which runs from Iowa Highway 139 at the Iowa state line and continues north to its northern terminus at its intersection with U.S. Highway 52 in Harmony.

Highway 139 serves as a north–south route between the Iowa state line and the city of Harmony.

The route passes near Niagara Cave.

Iowa renumbered its state highways that crossed into Minnesota in the early 1960s to match the Minnesota numbers.

[3] The entire route is in Fillmore County.