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 .

Before merging with Madiswil in 2011, Kleindietwil had an area of 2.68 km2 (1.03 sq mi). Of this area, 1.59 km2 (0.61 sq mi) was used for agricultural purposes, while 0.79 km2 (0.31 sq mi) is forested. Of the rest of the land, 0.28 km2 (0.11 sq mi) was developed, 0.02 km2 (4.9 acres) were rivers or lakes, and 0.02 km2 (4.9 acres) was unproductive land.

Of the developed land, industrial buildings made up 1.1% of the total area while housing and buildings made up 5.2% and transportation infrastructure made up 3.4%.