"I'm alive and well," Gorbachev said Wednesday night.
His denial came after state news agency RIA Novosti's two Twitter accounts posted reports of the death of Gorbachev, the first and last president of the Soviet Union.
The agency said they had been subject to a cyber attack by hackers and that the tweets were spotted and deleted within five minutes of being posted.
The messages were not the most convincing - one said: "Mikhail Gorbachev has died in the Shoko cafe in Yekaterinburg."
Another said he had died while talking to opposition politician Yevgeny Roizman, who is standing for mayor of the Siberian city.
Gorbachev, 82, has suffered health problems lately. In June, his spokesperson said he had been undergoing treatment in connection with his diabetes, while in April he was not well enough to travel to former British prime minister Margaret Thatcher's funeral in London.
In a statement on the website of Novaya Gazeta, the newspaper he co-owns, Gorbachev said he suspected the hackers were "carrying out the orders of some authorities" and that he had asked the paper to investigate who was behind it.