The decree, issued on the same day as Putin arrived in Iran on an official visit, said Russian firms were now authorised to export hardware and to provide financial and technical advice to help Iran with three specific tasks.
They were listed as helping it modify two cascades at its Fordow uranium enrichment plant, supporting Iranian efforts to export enriched uranium in exchange for raw uranium supplies, and helping Iran modernise its Arak heavy water reactor.
The decision follows a landmark deal between six world powers and Tehran in July, under which Iran agreed long-term curbs on a nuclear program that the West has suspected was aimed at creating a nuclear bomb.
The deal will lift international sanctions on Iran in exchange for at least a decade of curbs on the country's nuclear activity including reducing the number of centrifuges used to enrich uranium, and its enriched uranium stockpile.
Putin, who will attend a summit of gas exporting countries on Monday in Tehran, is also expected to meet Iranian President Hassan Rouhani and to discuss the Syria conflict.