Nazareth Hall Preparatory Seminary, known familiarly as Naz Hall, was a high school seminary in Arden Hills, Minnesota, United States, serving the Archdiocese of Saint Paul and Minneapolis. Founded in 1923 by Archbishop Austin Dowling, for most of its time Nazareth Hall educated students through four years of high school and the first two years of college. Over 600 alumni were eventually ordained to the priesthood. Due to declining enrollment and changing attitudes towards high school seminaries after the Second Vatican Council, it closed in 1970 with its collegiate functions being replaced by Saint John Vianney Seminary. The campus was sold and is now the site of the University of Northwestern.

In the early years of the Diocese of Saint Paul, its high-school and early college-aged seminarians were educated at a number of institutions. Many of the first seminarians of the diocese were tutored by bishop Joseph Crétin and other clerical teachers in the rectory next to the Cathedral of Saint Paul. In 1862, Bishop Thomas Grace opened the Ecclesiastical Preparatory Seminary of St. Paul in the former cathedral. In 1867, that institution merged with the coeducational cathedral school which operated in the same building. In November 1866, Grace purchased 40 acres (0.16 km²) on the shores of Lake Johanna for the purpose of establishing a permanent seminary. However, after the re-opening of the Benedictine St. John's College within the diocese in 1867, those plans were stalled and seminarians were educated either at St. John's or more distant institutions in the United States or Europe.

Grace's successor, John Ireland, took office in June 1884 and in December of that same year announced plans to build a seminary for the diocese which would become the University of St. Thomas. The fledgling college would function as a combination of a theological seminary, minor seminary, junior college, high school, and junior high school.

Following Archbishop Ireland's death in 1918, Austin Dowling became the Archbishop of St. Paul, and began to plan to separate the preparatory seminary from the College of St. Thomas, envisioning a secluded rural institution at the Lake Johanna property that would aid in recruiting both priestly candidates and financial supporters. On the first anniversary of the death of Archbishop John Ireland, Dowling established a fund to finance the building of a preparatory seminary. In the fund, $1,280,000 ($27.4 million in 2025) was raised specifically for the construction and endowment of the seminary. These plans were announced to the public in 1920, with the Romanesque-style campus estimated to cost $500,000 ($10.7 million in 2025) to construct, and planned to house 250 persons. The cornerstone of the new complex was laid by Dowling on May 21, 1922, in a solemn ceremony. The architects were Maginnis & Walsh of Boston, and the seminary was completed and dedicated by September 1923.

The redirection of diocesan funds and the withdrawal of minor seminarians had an impact upon the still-young College of Saint Thomas, as the 140 high-school age seminarians moving from St. Thomas to Nazareth Hall constituted nearly twenty percent of the student body at this time. Additionally, some within the archdiocese thought that the establishment of Nazareth Hall spread the resources of the archdiocese too thinly, and many criticized the separation of high-school age students as undesirable.

Timothy Crowley was the first rector of the seminary from 1923 to 1935. In its first year, there were 125 students. In the early years, the school struggled financially, operating at a deficit according to a 1929 report. Dowling was nevertheless resistant to hearing any criticism of his project, and furnished a personal suite at the school for his frequent retreats and visits there. As one priest of the archdiocese stated: "Nazareth Hall was the apple of his eye and woe betide the priest or layman who dared to utter an uncomplimentary syllable about the institution, its architecture, purpose, faculty or product. Every other institution in the archdiocese was a stepchild, seldom visited except officially."

Nazareth Hall covered six years of education—four years of high school and the first two years of collegiate studies. The remaining six years were done at Saint Paul Seminary. Coursework for the students included classes in Latin, Gregorian chant, math, the sciences, and social studies. Not all students who attended Nazareth ended up becoming priests, and so over time seminary leadership worked to make the curriculum suitable preparation for life outside of the priesthood.

Students produced a publication called Puer Nazarenus (transl. Boy of Nazareth) which contained pieces such as poems, stories, and a humor column. Students had basketball leagues, and played pool, handball, football, skating, skiing, table tennis, and other sports. Over time, the institution received a shorthand nickname of Naz Hall. The Sisters of Saint Francis (OSF) assisted with the domestic operations of the seminary and lived in one of the wings of the building.