The share-swap deal, which has been approved by boards of both exchanges, would bring in more synergies for BSE.
"We are in the process of getting approvals from the regulators and the High Court (for the deal)... It takes around 8 to 9 months for all this process to get over," BSE Chairman and Managing Director Ashishkumar Chauhan told PTI.
Besides, the deal has to be approved by the shareholders of the two bourses.
The loss-making United Stock Exchange (USE) is trading only in currency futures.
BSE is already a strategic partner in the exchange and was the single largest shareholder with nearly 15 per cent at the end of December 2013.
For the year-ended March 2014, USE posted a net loss of Rs 3.93 crore whereas it had a net profit of Rs 46.36 lakh in the year-ago period.
The exchange's net loss stood at Rs 2.47 crore in the three months ended March. In the same period a year ago, it had a net profit of Rs 56.41 lakh.
BSE, Asia's oldest bourse, late last year had launched trading in currency derivatives.
Apart from BSE, private sector lender Federal Bank is another major shareholder with about six per cent stake in USE at the end of December quarter. Other stakeholders, at that time, included Standard Chartered Bank (Mauritius) Ltd, HDFC Bank, State Bank of India, MMTC and Jaypee Capital Services.
