Leimiswil is a former municipality in the Oberaargau administrative district in the Canton of Bern in Switzerland . On 1 January 2011 Kleindietwil and Leimiswil were merged with the municipality of Madiswil .

Leimiswil has an area, as of 2009, of 4.65 km2 (1.80 sq mi). Of this area, 3.51 km2 (1.36 sq mi) or 75.5% is used for agricultural purposes, while 0.87 km2 (0.34 sq mi) or 18.7% is forested. Of the rest of the land, 0.25 km2 (0.097 sq mi) or 5.4% is settled (buildings or roads).

Of the built up area, housing and buildings made up 3.2% and transportation infrastructure made up 1.7%.