The two works, commissioned and owned by Hitler, were last seen at the end of the Second World War.
They are expected to make close to $100,000 in a single lot at Craig Gottlieb Auctions online sale between September 1 and 17.
Taken from Hitler's Berghof residence in Bavaria at the end of the Second World War, they are currently owned by a family of French-descent living in the US.
Auctioneer Craig Gottlieb believes that the works' rarity will help boost the price.
"These portraits are not rare - they are one of kind. So when it's the collector's one opportunity or the museum's one opportunity, sky is the limit." Gottlieb told US news outlet Fox.
Black and white photographs taken at the Berghof show the portraits on a wall.
"The photographs of the portraits that I found show they matched brush stroke for brush stroke. They are authentic. I would stake my entire reputation on it," adds Gottlieb.
The images of Klara and Alois Hitler were once well known in Germany, even appearing on postcards.
Neither parent lived to see their son's rise to power in Germany, both dying in the early 1900s.
Hitler himself was a prolific artist. A work attributed to him sold for £12,000 at Mullock's auction house in the UK last year.
Paul Fraser Collectibles will bring you the results from this auction in September.
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