St. John's Priory, Viborg (Danish: Johannitterklostret), was a monastery of the Knights Hospitaller in Viborg, Denmark.
The principal abbey of the Knights of St. John, otherwise known as the Knights Hospitallers, at Antvorskov established several small houses in towns throughout Denmark in the late 13th century, one of them at Viborg. Apparently the first small monastic house (Johannitterbo) was built at Viborg at St. Ib's Church, which had been given to Antvorskov Abbey. Eleven years later the priory, with its church rededicated to Saint John (Danish: Sanct Hans) was founded nearby in 1285 by the Count of Everstein, who gave a property in Viborg to the Order of the Knights of St John of Malta, or Hospitallers. His widow Mariana also gave additional income property to the priory to fund its operations, especially the hospital. Subsequently, confusion has arisen between St. John's parish church and St. John's Priory church.
The church formed the north range of a quadrangular abbey complex with refectory, dormitory, kitchens, guest house, and cellars. The church was 88 cubits long and 55 cubits wide, and was described by an observer as "grand". By 1527 a free-standing hospital (Sct. Hans Hospital) had been added to the complex. In 1458 a new larger building was constructed on the other side of St. Ib's Street.
St. John's Priory played a significant part in the Reformation in Denmark. Reform-minded Danes who had been to Germany and heard Luther or his ideas brought them back to Denmark in the mid 1520s. Among them was Hans Tausen, a Hospitaller who had studied in Germany and come back determined to spread the truth as he saw it to the people of Denmark. On Good Friday 1525 he preached Luther's ideas to the congregation at Antvorskov Abbey on Zealand, the headquarters of the Hospitallers in Scandinavia. The head of the order was scandalized by the rebellious monk and sent him to St. John's Priory in Viborg to contemplate his errors under the watchful eye of Prior Peder Jensen. Tausen eventually received permission to teach in the priory church and soon had a loyal and ardent following. His superior at St. John's protected him from the Bishop of Viborg who was prepared to arrest Tausen and put him on trial. But his ideas were too radical and he was expelled from his order and went to live with the Mayor of Viborg.