The British liner sank in international waters and so comes under no state's protection but, after a century, wrecks fall under the jurisdiction of a 2009 UN Convention on the Protection of Underwater Cultural Heritage.
"From now on, state parties to the convention can outlaw the destruction, pillage, sale and dispersal of objects found at the site," UNESCO said, in a statement from its Paris headquarters.
"They can take all possible measures within their power to protect the wreck and ensure that the human remains there are treated with dignity," it said.
The passenger liner Titanic hit an iceberg on its maiden voyage across the Atlantic, sinking to almost 4,000 metres in waters off Newfoundland on the night of April 14, 1912, with the loss of 1,514 people on board.
It was and remains one of the worst peacetime shipping disasters in history, and this year's anniversary is being marked by several cultural and historical events in Britain and the United States, its intended destination.
The wreck was rediscovered in 1985 thanks to advances in submarine technology, and historic artefacts have since been recovered.
"The sinking of the Titanic is anchored in the memory of humanity and I am pleased that this site can now be protected by the UNESCO Convention," said UNESCO director general Irina Bokova.
"But there are thousands of other shipwrecks that need safeguarding as well. All of them are archaeological sites of scientific and historical value. They are also the memory of human tragedy that should be treated with respect.
"We do not tolerate the plundering of cultural sites on land, and the same should be true for our sunken heritage," she said, calling on divers not to dump equipment or commemorative plaques on the Titanic site.