Oregon Route 140 is an Oregon state highway that serves the southern portion of the state. It runs from the community of White City, Oregon (just north of Medford), through Klamath Falls and on to Lakeview. It then continues east, eventually descending into the state of Nevada.

Oregon Route 140 begins in the city of White City, at a junction with Oregon Route 62 (which runs between Medford and Crater Lake National Park). Oregon Route 140 is the primary connection between Medford and Klamath Falls. The stretch of OR 140 between the two cities is known as the Lake of the Woods Highway No. 270 (see Oregon highways and routes), as it passes by the scenic Lake of the Woods and Mount McLoughlin in the Sky Lakes Wilderness. It then runs along the southwestern shore of Upper Klamath Lake, where it is part of the Volcanic Legacy Scenic Byway. Eventually, OR 140 enters the Klamath Falls area; it joins together with Oregon Route 66 (which runs between Klamath Falls and Ashland) on the Green Springs Highway No. 21, and the two highways soon intersect with U.S. Route 97 at a freeway interchange.

OR 140 continues east of here, on an alignment known either as the South Klamath Falls Highway No. 424 or the Southside Bypass. Southeast of town, OR 140 intersects with Oregon Route 39, heads north on a shared alignment for about two miles (3 km), on the Klamath Falls-Malin Highway No. 50, and then continues east towards Lakeview on the Klamath Falls-Lakeview Highway No. 20.

In Lakeview, the highway intersects with U.S. Route 395 over the Fremont Highway No. 19 and then continues east on the Warner Highway No. 431 eventually dropping down into Nevada. Oregon Route 140 ends at the Nevada state line, where it becomes State Route 140.