OM said the news was "unexpected" but followed surveys by the ship's classification society RINA which found the structure in need of "significant" additional work before its certificates could be renewed. Its current certificates are due to expire at the end of 2009.
The amount of work needed to bring the vessel up to RINA's standards was estimated at around £10 million.
OM said it was unwilling to invest that amount of money in a ship that is already 95 years old – the oldest ocean-going passenger vessel still in operation in the world.
The ship was first launched in 1914 as Medina before it came into the hands of OM in 1977, when it was fitted up for Christian mission service and renamed Doulos, the Greek word for servant.
Since then, the ship has been used to bring the message of the Gospel and educational resources to more than one hundred countries. It will end service on December 31.
The 300-strong crew is made up entirely of volunteers from more than 40 countries. The head of OM Ships International, Peter Nicoll, said his immediate priority was to resettle the crew members.
OM's other ministry ship Logos Hop, which was launched earlier this year, continues to draw huge crowds in the Caribbean.
OM said it "remained committed to operating a two-ship ministry" and is looking into the short-term hire of another vessel while a replacement for Doulos is sought.
Mr Nicoll asked supporters of OM Ships to pray for Doulos' replacement.
OM is taking donations towards Doulos' replacement at www.omships.org/donate. Donations should be marked 'Doulos Project'.