William Bouguereau's Frere et Soeur, an oil painting of a young woman tenderly holding her baby brother, could fetch up to 1.5 million dollars (950,000 pounds) at Sotheby's on November 4.
It was painted in 1887 by the French artist, whose work is enjoying renewed interest. Moore's other painting, Mere et Ses Enfants by Belgian painter Alfred Stevens, is estimated to bring up to 200,000 dollars.
"With the renovation and new direction our home is taking, it is time for a change," the Telegraph quoted Moore as saying.
The actress acquired the works in 1995 at a Christie's auction, paying 178,500 dollars for Frere et Soeur and 200,500 dollars for the Stevens painting.