Andrei Zamyatnin had been working as a guest researcher at the Swedish Agricultural University in Uppsala when he was detained on February 15.
Prosecutor Tomas Lindstrand said Zamyatnin had gathered research material from the university and passed it to an employee at the Russian Embassy in Sweden.
But he said Zamyatnin could not be charged with espionage because the material did not pose a threat to Sweden's national security or armed forces.
Russia had repeatedly demanded Zamyatnin's release.
(AP, Interfax, ITAR-TASS)