The Book Of Hours has an enamelled gold metal cover studded with gems such as rubies, turquoise and tourmaline and contains parchment painted with 20 religious images and prayers to be said throughout the day.
A popular Christian devotional item in the Middle Ages, this particular prayer book belonged to Francois I of France.
It was made in 1532 and has been purchased by an overseas buyer for £8m.
Culture minister Ed Vaizey has placed a temporary export bar on the Book of Hours to give a UK buyer time to come up with £8 million to save it for the nation.
He said: "This exceptional book provides us with a rare glimpse into the royal courts of 16th century Renaissance France and is of outstanding scholarly value.
"I hope that this unique book remains in the UK for the public to enjoy."
