Slovenia will sign the agreement in June, Slovenian Economy Minister Matej Lahovnik said at a news conference in Ljubljana.
The South Stream pipeline will transport Russian natural gas via the Black Sea and Bulgaria to Italy.
"Slovenia has made this decision and wants to be a part of this project. We are working on a final text of the agreement and we expect its signing in June," Lahovnik said after meeting Igor Shchegolev, the Russian Minister of Telecommunications and Mass Communications.
Lahovnik said that the two countries had worked on the agreement for a long time and now their finance ministries should elaborate details relating to the tax status of a joint Russian-Slovenian pipeline construction and management company in Slovenia.
The two ministers discussed the matter during a meeting of the joint Russian-Slovenian commission for trade and scientific and technical cooperation in Ljubljana.
Russian Energy Minister Sergei Shmatko was quoted by Reuters as saying that "in the last two or three weeks, we've held a series of negotiations with Austrian and Slovenian partners about an intergovernmental agreement."
"This document is at an advanced level of preparation," he said.
An agreement on establishing a joint company for the construction of the South Stream gas network was signed in the Russian Black Sea resort of Sochi on 15 May between Russian Gazprom and companies from Greece, Serbia, Bulgaria and Italy.
Moscow seems determined to push for the South Stream and thus "outpace the rival, Western-backed Nabucco pipeline," Reuters reported. Nabucco would supply gas from sources other than Russia.