LONDON, Jan 21 (Reuters) - Investment company Franz Haniel & Cie GmBH [FAHNIN.UL] placed a 500 million euro ($710.2 million), seven-year bond on Thursday to pay down bank debt used to buy a stake in Metro AG (MEOG.DE), the world's third-biggest retailer.

"With aggregate demand reaching more than 3.6 billion euros, the bond was seven times oversubscribed," Haniel said.

Stefan Meister, a member of Haniel's managing board, said: "We are using the bond to decrease bank liabilities and thus underpin our financing structure."

Specifically, the money will help Haniel pay back the rest of the debt taken on to acquire a 16 percent stake in Metro in 2007. Haniel currently holds a controlling 34.2 percent stake in the retailer.

Managing banks on the deal are BayernLB, Calyon, Helaba, LBBW and UniCredit. The bond has a coupon of 5.875 percent.

The bond is the second by Haniel -- which also has a controlling stake in Europe's biggest drug distributor, Celesio (CLSGn.DE) -- after the successful completion of a maiden, 1 billion-euro bond last October.

($1=0.7040 euro)

(Reporting by Simon Jessop)