The article examines the specific character of the process of secularization of the Order's possessions in the Baltic region. It explores the formation of the Duchy of Courland and Semigallia as a result of secularization of possessions of the Livonian branch of the Teutonic Order. The first half of the 16^th century had brought about political and religious changes of great importance to the Baltic States, which had been associated with the spread of Protestantism in the region. Protestant duchies were formed out of the possessions of the Catholic religious-military corporation. The article focuses on religious questions in general and King Sigismund's guarantees to the classes professing Lutheranism, in particular. First implemented in 1525 by the Prussian Grand Master, Albrecht von Brandenburg-Ansbach, secularization was then carried out in 1561 in Livonia by landmaster Gotthard von Kettler. The process had resulted in the disappearance of Ordensstaat as a political entity and changes in the political map of the region. The article also analyses the meeting of the Order's gebietigers on April 5, 1560, reflecting the mood within the religious-military corporation before secularization, which was connected with the military and political situation caused by the Livonian war, and religious issues. The given examples signified the beginning of the age of Confessionalization as early as the mid-twenties of the XVI century, i.e. somewhat earlier than it had been asserted in historiography).