Kleindietwil 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.

[1] Before merging with Madiswil in 2011, Kleindietwil had an area of 2.68 km2 (1.03 sq mi).

28.4% of the total land area is heavily forested and 1.1% is covered with orchards or small clusters of trees.

In the 2007 election, the most popular party was the SVP which received 39.2% of the vote.