Werthenstein is a municipality in the district of Entlebuch in the Canton of Lucerne in Switzerland .

Werthenstein has an area of 15.7 km2 (6.1 sq mi). Of this area, 59.6% is used for agricultural purposes, while 32.4% is forested. Of the rest of the land, 6.9% is settled (buildings or roads) and the remainder (1.1%) is non-productive (rivers, glaciers or mountains). In the 1997 land survey, 32.38% of the total land area was forested. Of the agricultural land, 56.28% is used for farming or pastures, while 3.31% is used for orchards or vine crops.