The theme of this article is the analysis and edition of a Letter of Good Birth (legitimization certificate) issued by Dean Tymoteusz Łowczany and Lutheran Consistory of the Duchy of Cieszyn. The Certificate confirms that Jan Pragenus was legitimate child, born in wedlock of Jerzy and Małgor-zataThe Letter of Good Birth of Jan Pragenus is undeniably very precious because of its selection of facts.This is the unique document, known today, drawn up by the Consistory that is, at the same time, evidence of a two-level organizational structure of the Lutheran Church in the Duchy of Cieszyn in times of the Reformation.Even when biographic details of Jan Pragenus have not brought new findings, the very novelty is a well preserved seal the matrix of which was made in the beginnings of the XVII century.