Two years ago, this small bag was bought for $995 US dollars. Now, it's going on sale and could be sold for $4 million dollars! So what's so special about it?
On the Apollo 11 mission in 1969, US astronaut Neil Armstrong became the first person to ever walk on the moon.
He collected 12 pieces of rock and nearly 500 grams of material from the surface of the moon and kept it safely in this bag.
The moon dust and rocks were sent to a lab where the bag was thought to be lost.
Years later, the bag turned up on an auction website and was bought, along with some other items, for $995 dollars by Nancy Lee Carlson.
She sent it off to Nasa to be tested, where they found traces of moon dust still on it!
This year, on the anniversary of the Apollo 11 mission in July, the bag will go in the Space Exploration auction at Sothebys in New York, America.
As the most important item at the auction, we'll have to wait and see how much it sells for!