The offer will include an issue of new shares as well as some of the shares owned by the bank's private equity investors, said three sources. All the sources declined to be named as the details of the IPO are not public yet.
The bank's shareholders include International Finance Corp, an arm of the World Bank, CDC Group of Britain, Norwest Venture, Beacon Private Equity, Samara Capital, IDFC Private Equity and Aditya Birla Private Equity, according to the bank's website.
The bank has expanded its business into India's poor rural areas, a tough market long neglected by the country's financial groups.
Ratnakar, with roots in parts of Maharashtra, makes about one third of its loans to farmers, small businesses and low-income consumers - a target base that normally operates outside India's banking system.
The lender will within a week hire at least four banks to manage the public offering, two of the sources said. At least 10 banks are in the race to win the mandate for the IPO process, they said.
Ratnakar Bank last year said it was considering an IPO and Rajeev Ahuja, head of strategy at the bank said on Tuesday the launch would depend on market conditions, adding that Ratnakar was "well capitalised" for the next 12-15 months.
On how much Ratnakar is looking to raise from the listing, Ahuja said the equity dilution would depend on the growth capital needs of the bank. He said nothing had been finalised.
Ratnakar Bank's share offering will be the first Indian bank listing on domestic bourses since state-owned Punjab & Sind Bank raised $105 million through an IPO in 2010, according to Thomson Reuters data.
The bank's IPO is expected to follow a raft of equity sales by Indian companies in the coming months on the back of growing demand for equities after a landslide election victory for new Prime Minister Narendra Modi.
Economic downturn and sluggish corporate earnings growth in Asia's third-largest economy have deterred equity deals in the past year.
Prime Minister Modi's Bharatiya Janata Party last month won India's first outright parliamentary majority in three decades, spurring hopes of a revival in an economy that is witnessing its longest spell of under-5-percent growth since the late 1980s.