Ciftci joined Dundee United on a two-year deal in the summer and the Turkey youth international has scored seven goals in 16 appearances for the club.
The new deal will keep Ciftci at Dundee United until the summer of 2016.
Dundee United boss Jackie McNamara said: "Such has been the impact of Nadir, I felt it was important to move quickly and offer the extension. He has fitted in so well, not just on the park but also in the dressing room.
"His ability is aligned with his desire to improve as a footballer and he wants to do this at Dundee United.
"His performances and goals have helped the club progress and with this commitment to a longer-term contract, Nadir has shown his desire to be part of what we are building at Tannadice."
Ciftci added: "From the first day at training I knew I would enjoy being at Dundee United and over the first few months of the season this has proved to be the case. It was an easy decision for me to extend my contract.
"The team is playing great football and we have a chance to grow even better. It is exciting to be part of this team and I have also been delighted with the response of the United fans to my style of play.
"Signing this contract extension allows me to focus on improving as a footballer and this is the best place for me to do so right now."