The Diocese of Qui Nhơn (also written as the Diocese of Quy Nhơn; Latin: Dioecesis Quinhonensis; Vietnamese: Giáo phận Qui Nhơn) is a Catholic diocese in central Vietnam.

The Bishop is Matthieu Nguyễn Văn Khôi, previously rector of Assumption Cathedral in Quy Nhơn and professor at the Stella Maris Major Seminary of Nha Trang, was appointed Coadjutor Bishop of the diocese by Pope Benedict XVI on December 31, 2009.

The creation of the diocese in present form was declared on 24 November 1960.

The diocese covers an area of 16,200 km², and is a suffragan diocese of the Archdiocese of Huế.

By 2004, the diocese of Qui Nhơn had about 62,520 Catholics (1.7% of the population), 70 priests and 36 parishes.