The company said it was still interested in flying Dreamliners and was in talks with a view to leasing them before 2014. It added that the results of the talks would be announced later.
S7 gave no reason for scrapping the May 2007 contract, worth an estimated $2.4 billion. Deliveries of the planes were due to start in 2014.
Boeing said it regretted the termination of the contract, which it linked to the ongoing financial crisis.
However, Boeing spokesman Dmitry Khrol said the company "is still in daily contact with S7, which remains an important client."