Chhagalnaiya is a Upazila (Sub-district) of Feni, Bangladesh.

It lies in the southern part of the district, bordering Tripura state of India and Mirsharai Upazila of Chittagong. It is rich in history and culture. The great medieval warrior Shamser Ghazi hailed from Chhagalnaiya. It is also the birthplace of many other noted historical figures including Sir A. F. Rahman, first Muslim Vice Chancellor of Dhaka University, Gaziul Haque, Advocate Kazi Fazlul Haque and Riaz Rahman.