The focus of the collection lies on the one hand on the representative stock of Swiss little masters (e.g. Lory, Aberli, Lafond or Wocher). On the other hand, the art museum also has works of Swiss creative artists from the 19th and 20th centuries, such as Ferdinand Hodler, Cuno Amiet, René Auberjonois, Paul Klee, Otto Morach, Johannes Itten, Alfred Glaus, Otto Nebel, Varlin and Meret Oppenheim. The core of the collection includes works from Swiss pop art and photorealism. The collection is also always expanded by works of contemporary artists, as illustrated by the acquisitions of the works of artists such as Balthasar Burkard, Karim Noureldin, Claudio Moser, Claudia & Julia Müller or George Steinmann.

The basic stock of the collection consists of a series of paintings that come from the various departments of the municipal administration. The Landammann Carl Friedrich Ludwig Lohner also gifted the museum a comprehensive collection of graphic sheets. Later, a collection of Thun Vedutas (mainly Swiss little masters) followed and hand drawings and graphic works of the painter Werner Engel of Thun. The remarkable work of the painter Fred Hopf could also be acquired by bequest.

Other private donations were added from the 50s onwards:

• 1950 and 1956: Hans Lüthi-Hefti, the first donor in Thun, bestows part of his collection

• 1951: Alfred Glaus hands over his complete lithographic works

• 1990: More pictures arrive at the museum through the heirs of Alfred Glaus

• 1959: First loans from the federal government and other gifts from various creative artists

• 1971: Karl Geiser and Ernst Morgenthaler

• 1972: Karl and Ruth Stauffer

• 1976: Olga and Ruth Mayser

• 1977/81: Victor Surbek and Marguerite Frey-Surbek

• 1981: Rudolf Mumprecht

Many other donations followed. The Supporting Association of the Kunstmuseum Thun has enabled numerous other acquisitions since its inception around 1959.

Acquisitions of works of artists from the region endow the collection with a special character. The monochrome works by Peter Willen (born 1941) or the photographs of the Thun-based artist Chantal Michel (born 1968) count among the highlights of the comprehensive collection with around 7,000 works.