The airline has committed to order 20 737-800s, a version of the plane Boeing is making now. Turkish also plans to buy 40 737 Max 8s and 10 737 Max 9s, which is a planned new version of the plane which will have new engines.
The deal would be worth $6.9 billion at list prices, although discounts are common. It also includes options for another 25 737 Max 8s.
Boeing said it would work with Turkish to finalize the order.
The 737 is Boeing's smallest but most popular plane.