In Casa Haartman, there are several works by Wäinö Aaltonen. This is due to the friendship between Axel and Wäinö Aaltonen, and many of the works were gifts from Aaltonen to Axel and Hedvig.

Aaltonen and Haartman became acquainted as early as 1910 when Aaltonen was studying at the Turku Art School, where Haartman was a teacher. Later, Haartman became the commissioner for Aaltonen's first solo exhibition abroad, held in Stockholm in 1927. The exhibition was a great success.

In the hall, there is a work by Aaltonen. It is a bronze portrait of Axel Haartman, created in 1919. During the work on the portrait, Aaltonen was concerned that the portrait would appear too "stingily" beautiful, but fortunately, it turned out that Axel's eyes were positioned at slightly different heights, which resolved the issue.

In the dining room, there is a cubist version of Aaltonen's Aleksis Kivi Statue. This was a gift from the artist to Hedvig Haartman on her 60th birthday.

Wäinö Aaltonen also gifted his self-portrait, painted in oil with elements of gold leaf, to Axel on his 50th birthday. That portrait is no longer part of Casa Haartman's collection, as Axel donated it to the Wäinö Aaltonen Museum (now WAM) in 1967 when the museum was inaugurated.