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.

Of the rest of the land, 0.25 km2 (0.097 sq mi) or 5.4% is settled (buildings or roads).

17.0% of the total land area is heavily forested and 1.7% is covered with orchards or small clusters of trees.

Most of the population (as of 2000[update]) speaks German (95.9%), with Albanian being second most common ( 2.0%) and Portuguese being third ( 0.9%).