"Online news sites that report regularly on issues relating to Singapore and have significant reach among readers here will require an individual licence," Singapore's Media Development Authority (MDA) said in a statement.
"This will place them on a more consistent regulatory framework with traditional news platforms which are already individually licensed," the media regulator said.
Prosperous and orderly Singapore, a regional base for many multinationals and fund managers, is one of the world's most wired-up cities with most people having broadband access.
It has long maintained strict controls on the media, saying that was necessary to maintain stability in a small, multi-racial country and that media must be held accountable for what they publish.
Lobby group Reporters Without Borders, in its latest report, ranked Singapore 149th globally in terms of press freedom, down 14 places from 2012 and below many of its neighbours.
In 2011, the city-state's tiny opposition made big gains against the long-ruling People's Action Party in parliamentary elections, partly by using the Internet to reach voters.
A survey by the Straits Times newspaper shortly before the vote found 36.3% of people between the ages of 21 and 34 cited the internet as their top source of domestic political news compared with 35.3% who preferred newspapers.