The Roman Catholic Diocese of Tianjin is a diocese located in the city of Tianjin in the Ecclesiastical province of Beijing in China.

Data from 1950 indicated there are 50,000 registered Roman Catholics in Tianjin, occupying 1.4% of the total 360,000 population; recent data from 2008 refleted a recovery of presumably 100,000 Catholics after years of persecution within which 40,000 are officially registered and 60,000 is the estimated number of underground faithful. Even that was considered, it is still only a very tiny proportion of the current 15,000,000 population(0.7%).

The church was a Catholic Church built at the request of a French missionary, Xie Fuyin in 1896. Considered as a haven for orphans and young children, the church, in fact, caused great harm to Chinese children. In June 1870, angry residents of Tianjin City swarmed to the church to find out why the church abused scores of children, sometimes beating them to death. As a result, the French consul shot Tianjin County Magistrate Liu Jie, injuring his retinue. The people of Tianjin, in turn, beat up the consul and his secretary and burned down the church, including other French, English and American churches, and the French consul's office. The incident is known today as the Tianjin Church Incident.

In 1893, imperialists used the indemnity to rebuild Wandhailou Church and other churches. During the Boxer Uprising in 1900, the church was once again destroyed. The existing church was rebuilt for the third time in 1904.

Facing southward, Wanghailou Church is a 56-by-15 meter post and panel structure. At the front are three tower buildings, 22 meters high and shaped like penholders. Two interior posts reflect the typical style of the French Catholic church.