"Russia is a member of international agreements under which marijuana is a prohibited drug. Russia will adhere to its international obligations in this sphere," Putin said during a Web cast.
He said the legalization of soft drugs in a number of countries had not reduced the use of hard drugs such as heroin.
He said drug dealers faced tough penalties under Russia's Criminal Code.
"The question is not about tougher punishment but ensuring that punishment is inevitable," he said.
About 100,000 Internet users voted for the question about legalizing soft drugs in Russia.