The article presents economical basis of the Dominican monastery in Sieradz at the beginning of the 17th century. The main source for the subject is the register of the monastic income found in the monastic cartulary kept in the Archives of the Dominican Fathers in Cracow. The income of the Dominican monastery in Sieradz at the beginning of the 17th century consisted of privileges, the most important of which was the right to collect one fifth of the malt measure from the royal mill, the right to catch fish in the Warta river and the profits from the butchery. Moreover the Dominicans earned income from the perpetual ground rent from town houses they owned. Gardens and meadows in the possession of the monastery were also of great significance for the monastic economy. However the greatest share (about 92%) in the upkeep of the Dominicans in Sieradz was earned from rents secured against land property. The analysed source does not contain full information about monastic income. Income from pastoral activity and collections in the monastic district was not registered. On the basis of the gathered data, however, it can be stated that at the beginning of the 17th century the monastery was in a good financial condition, which facilitated its fast development at that time.