The article describes the history of the Polish organization 'Uniao Juventus'. Created in 1898 in the city of Curitiba, it was the biggest and most important association of the Polish community in Brazil. During the past 100 years 'Uniao Juventus' has changed its name, structure and the main goals, but it preserved some of its Polish characteristics. The transformation of 'Uniao Juventus' is analyzed within the conceptual framework of assimilation processes among Polish immigrants in Curitiba.