Teresa Amatller continued to live on the main floor of Casa Amatller after the death of her father in 1910 until her death in 1960. In order to preserve Casa Amatller and all its heritage, he had created the Fundació Institut Amatller d’art Hispànic in 1943, which would be in charge of managing the building.
One of the objectives of the Fundació Institut Amatller d’art Hispànic was to promote research into the history of Hispanic art. After Teresa Amatller’s death, the former home of the industrial chocolatier and his daughter was transformed into a study centre of the Institut Amatller d’Art Hispànic with a library open to the public, specialising in Spanish art.
The good aesthetic criteria of the board of trustees and Josep M. Gudiol, the institution’s first director, made it possible for all the interventions that had to be carried out to be reversible, respecting all the architectural and ornamental heritage of the modernist house: shelves were fitted out on all the possible walls, including inside the monumental fireplace in the living room; the dining room became the researchers’ reading room; the original modernist furniture and the art collections were concentrated in two rooms.
The headquarters of the Institut Amatller d’Art Hispànic operated uninterruptedly on the main floor of the Casa Amatller until 2009, when it was decided to open the building as a Casa Museu.