Kept in a miniature coffin, the cloth was estimated to go under the hammer for between 4,000 and 6,000 euros.
The 20 cm by 16 cm (8.9 by 6.3 inches) fabric was accompanied by a handwritten piece of paper that said: "The precious blood of Louis XVI, 21 January 1793" -- the day he was guillotined in the heart of Paris.
The Coutau Begarie auction house said the cloth had been scooped by a French collector who is fascinated by the former monarch.
Parisians had jostled to take souvenirs after the execution including snippets of his hair. They also dipped their garments or cloth in the pool of blood left near the guillotine.
The small coffin also included a small pouch of sand which an expert said had "probably been collected from the ground at the foot of the guillotine where the king was beheaded".
He added, however, that only a DNA test on the sample of the stained cloth could prove if it really contained Louis XVI's blood.
A silver buckle from the king's shoe was sold for around 4,400 euros to the same collector.