Armed thieves burst into the Chacara do Ceu museum in Rio de Janeiro on Friday and walked off with paintings by Picasso, Matisse, Monet, Dali as well as a book by Picasso.
They used the cover of carnival crowds to make their escape.
Experts said the art works were worth between A$27.11 million (US$20 million) to A$67.79 million (US$50 million).
The Association of Friends of the Chacara do Ceu museum and the National Historic and Cultural Heritage Institute is offering the reward in the hope that the valuable works will be returned to the museum.
A telephone hotline has been set up for information on the heist, but police said that callers’ identities could remain confidential.
Police have also issued computer-generated images of two of the armed thieves and have also given details of the stolen works to 182 countries through Interpol.
At least four men were believed to have been involved in the theft.
The paintings included Pablo Picasso's The Dance and a book by him entitled Toros, Claude Monet's Marine, Henri Matisse's Garden of Luxembourg and Salvador Dali's Two Balconies.