Oyen leaves Forest
The 28-year-old joined the East Midlands club on a free transfer in January 2003 but his career in English football has not worked out as he wished.
Oyen has suffered from injury problems while at Forest - including a knee injury - and despite being fit to play again, the former Genk, PSV Eindhoven and Anderlecht man has not figured in Joe Kinnear's plans.
The defender admitted that his family were keen to move back to Belgium and Oyen hopes he can kick-start his career back in Belgian football.
"It's a pity that things have not worked out for me in England and it is probably best for everyone concerned that I return home," Oyen told Forest's official website.
"My family are keen to get back to Belgium and I am determined to find a club there and revive my career.
"I really want to be somewhere where I have a chance of regular first team football and the best option for that would appear to be in Belgium.
"I have no regrets about trying to be a success in the English game with Forest and I am sorry it has not worked out."