This article is an announcement of edition of source material, entitled Register of Gdansk’s Catholics in First Half of 17th Century. Register now includes the period from year 1608 to 1640 and ca. 2550 names of people, who received sacraments (baptism, matrimony) or who were buried in the parish of St. Bridget in Gdansk (Old Town). These data were influenced by Jesuits because they initiated the implementation of the register books in this church and led official and unofficial ministry in it until forties of 17th Century. Unfortunately data from other Gdansk’s churches didn’t preserve to our time. We can only additionally use the single data from some suburban parishes. It should be noted, that the collected source material includes 89% (2265) people, who appeared only once in these register books as parents, children, godfathers (mothers), witnesses, brides, grooms, etc. This proves, that they rather temporarily lived in Gdansk and the Catholic minority in this city was rather unstable. The rest of the Catholic population (11%) included people who repeatedly were in the role of parents, godfathers (mothers), witnesses. They were representatives of the wealthier Catholic families in Gdansk and were the germ of new municipal quasi-elite of Catholics inside the large protestant city. In conclusion, Register of Gdansk’s Catholics is a very good auxiliary source material, which can be used to the demography, socio-topography, prosopography and genealogy research. It can be especially used to the research on religious identity of communities, which represented different religious face.