Turkish Airlines, which earlier firmed up 15 options for Boeing 737 aircraft, will take delivery of 10 737-800s and five 737-900ERs.
The order has a list price value of more than $1.2 billion, says Boeing.
Turkish Airlines ordered 10 737-800s and 10 737-900ERs in 2010, and said then it was taking 15 options. It said last month it would firm up these options, which would be delivered between 2013 and 2015.
The airline's new 737s will come with the Boeing Sky Interior.
"These new Boeing 737 aircraft will help us to reach even more cities and build a truly global network," says Turkish Airlines CEO Temel Kotil.