The main objective of this paper is analysis of the regulatory framework and the practice of naturalization in Croatia and Slavonia from 1848 to 1918. In his work the author has used the domestic and foreign literature, legislation and archives. In the paper the author has pointed out that in the feudal period local naturalization was a very important way of acquiring domestic status (indigenat). Changes in the system of naturalization have occurred after breakdown of Revolution 1848 when Austrian model of citizenship was introduced in Croatia-Slavonia. The Austrian model of citizenship was based on supremacy of state citizenship over local citizenship. That way the earlier ways of local naturalization were abolished. The new rules on naturalisation were introduced in Croatian-Slavonian legal sistem during Bach's absolutism in 1853 by Austrian General Civil Code (AGCC). The author argues that these rules remained in force after the collapse of absolutism in the period of provisional constitutionality from 1860 to 1868. Moreover, the model of naturalization established by AGCC was with some modifications maintained even later in the period of Hungarian-Croatian citizenship from 1868 until 1880. The regime of naturalization established by AGCC was finally abolished 1880 when the Law of December 20, 1879, concerning the acquisition and loss of Hungarian citizenship entered into force. By this new Law the system of naturalization was regulated very systematically and in detail what was quite opposite to previous regulation. Analyzing the practice of naturalization the author has demonstrated that the practice of naturalization in the entire period was open, inclusive, if the applicant proved all legal requirements for naturalization.