The Media Development Authority, which regulates the Internet, said in a statement last night that it has blocked access to the Canada-based website because it is in "flagrant disregard of our family values and public morality."
Will therefore not allow Ashley Madison to operate in Singapore and have worked with Internet service providers to block access to the site," the statement said.
AshleyMadison.Com started in Canada in 2001. With the slogan "Life is short. Have an affair," it has attracted more than 20 million users.
Some citizens, however, disagreed with the ban.
"What will the government ban next? A movie about adultery? An erotic novel? It's just plain silly and not having this website around doesn't mean people still can't cheat if they want to," said Shalini Nair, 35, who has been married for six years.
Ashley Madison has reportedly said it will explore legal means to overcome the ban.