It was erected as an apostolic vicariate on 12 November 1934, with territory taken from the mission of Yenchow (q.v.) and entrusted, like the mother mission, to the Society of the Divine Word. On 11 April 1946 it was raised to the status of a diocese, a suffragan of Tsinan. Over an area of 13,000 sq. km., it counted, as of 30 June 1950, approximately 4,000,000 inhabitants, of whom 74,013 were Catholics, served by 59 priests, including 12 Chinese, and 49 sisters, 45 of them native. It had a seminary, 6 schools, 32 works of charity and beneficence.
The first evangelical preaching in the territory of Tsaochow came after the arrival of the Divine Word Missionaries in the southern region of Shantung, which occurred in 1882. It was the first apostolic vicar of the region, Bishop Johann Baptist von Anzer (1886–1904), who attempted in vain to penetrate into Tsaochow, just as the efforts of Fr. Giuseppe Freinademetz to enter Tsachisen proved fruitless. At Changkiachwang, in 1897, Fathers Franz Nies and Richard Henle were killed. Subsequently, the mission experienced considerable growth: by 1934, the year of the erection of Tsaochow, there were 47,000 Catholics and 9,000 catechumens, served by 33 priests, 6 of them Chinese.