Louisiana Highway 20 (LA 20) is a state highway that serves Terrebonne Parish, Lafourche Parish, and St. James Parish. It spans a total of 36.6 miles (58.9 km)as a two lane, undivided road.

From the south, LA 20 begins at LA 182 in the northwest Terrebonne Parish town of Gibson. The road parallels then intersects U.S. 90 (Future I-49) at two locations (Exits 189 & 194) as it heads northeastward, where it intersects LA 24 in Schriever. LA 20 turns due north and intersects LA 1 in Thibodaux as it continues northward. The road then passes through Chackbay before it enters St. James Parish. LA 20 runs northward through South Vacherie and ends at an intersection with LA 18 in North Vacherie.