The diocese of Long Xuyên () is a Latin Catholic diocese of Vietnam. The current bishop is Joseph Trần VÃÂn Toản, since 2019.
The creation of the diocese in present form was declared November 24, 1960.
The diocese covers an area of 10,243 kmò, and is a suffragan diocese of the Archdiocese of Ho Chi Minh city.
By 2016, the diocese of Long Xuyên had about 247,000 believers (5.9% of the population), 275 priests and 186 parishes.
Queen of Peace Cathedral in Long Xuyên town has been assigned as the cathedral of the diocese.