Navalny was flown from Russia to Berlin in August after falling ill on a domestic flight. He received treatment in the Charite hospital for what Germany said was poisoning by a potentially deadly nerve agent before being discharged in September.
"I claim that Putin is behind the crime and I don't have any other versions of what happened," Navalny told Der Spiegel, according to an extract of an interview due to be published later on Thursday.
The West has demanded an explanation from the Kremlin, which has denied any involvement in the incident and said it has yet to see evidence of a crime.
"You don't feel any pain but you know you're dying," Navalny said of the moment that the nerve agent began to take effect on him.
Navalny told Der Spiegel he would return to Russia, adding: "My task is now to remain fearless. And I have no fear!"
A political activist who helped bring Navalny to Germany has said on Sept. 24 it would take the Russian opposition leader at least another month to regain fitness, adding it was clear he planned to return to Russia and resume political activity.