The Virginia-based space travel firm, which is the only company to have booked and offered commercial rides to the International Space Station, will double the room in the Soyuz spacecraft for the flights.
Soyuz spaceship, which was provided by Russia's Federal Space Agency, has carried seven passengers since 2001 to Space.
A trip for two around the moon in the bigger spaceship will cost around $150 million per passenger.
According to Space Adventures, the circumlunar trip will require at least two months of training to help familiarize the passengers with spacecraft and the outer space environment.
As commercial space travel continues to draw private investment, Space Adventures officials expect the lunar trip to be a landmark in the history of space exploration.
The moon holds a special place in all of our hearts. It's a symbol of the space future that humanity wishes for, a symbol of our curiosity, and something that we see every night. When the private moon mission launches, the eyes of the world will truly be upon those people, and it will truly be an extraordinary event, said the company's chairman Eric Anderson.