The first issue of Kalameh Sabz (Green Word) carried pictures of both Mousavi and the former reformist president Mohammad Khatami who is backing the ex-premier in his presidential bid.
"Kalameh Sabz is aimed at creating a mirror-like newspaper, to show who we are and what we stand for and to guide us in finding our path," said the first editorial written by Ali Reza Hosseini Beheshti, the paper's chief editor.
"We want to have a paper that offers a different perspective and urges the people to actively decide their fate."
The 16-page daily is being sold for about 30 cents — an average price for Iranian papers — and covers variety of topics, but focuses mainly on politics. The election campaign begins formally on May 22.
"The paper reflects Mousavi's views," an administrator in the newspaper, Ebrahim Pashena, told AFP.
"It has a start-up circulation of 40,000 but we think it will eventually reach several hundred thousand," he said, adding that Kalameh Sabz is being distributed nationwide.
Mousavi, who is backed by reformist groups, has emerged as one of the main opponents of hardline incumbent President Mahmoud Ahmadinejad who is seeking a second term in office.
The last prime minister of Iran before the post was scrapped in 1989, Mousavi is seeking to make a comeback after two decades in the political wilderness.
