The article aims at describing the situation of Polish language in Lithuania in the beginning of 20 century as it was described in the novel 'Unia' by J. Weyssenhoff. The authoress tries to evaluate credibility of this source and its value for studies of Polish language spoken in Kowno region. She reminds that the novel (published in1910) was written when the Polish-Lithuanian conflict was growing and Polish language was endangered not only by the partitioner but also by national Lithuanian movement. Special attitude is paid to the picture of Polish in the Kowienszczyzna region where linguistic and national problems were known to Weyssenhoff by personal experience. The authoress describes this complicated picture: classification of Polish variants proposed by Weyssenhoff, the weakening condition of Polish language and various threats to it. She shows that Weyssenhoff's description provides an interesting documentation, valuable because we do not have other sources concerning this part of the region.