The effect of urbanisation on parasite prevalence, especially these associated with human diseases, such as Lyme borreliosis, is of high interest. The blackbird Turdus merula is a ground-feeding species particularly predisposed to constitute a Borreliella spp. (Lyme borreliosis causative agent) reservoir. So, the aim of the study was to examine if the tick infestation level and their Borreliella spp. infection prevalence differs in blackbirds resident in two disparate habitats in Poland – one highly urbanized (in Warsaw agglomeration) and the other forested (in Mazurian Lake region). The infection in ticks feeding on blackbirds was ascertained based on detection of bacterium DNA (PCR). The prevalence of tick infestation in urban and forest-living blackbirds was similar (90 and 91.7%, respectively) but the mean number of parasites per bird was markedly greater in the forest (4.0 ind.) than in the urban populations (1.5 ind.). Even though, the Borreliella spp. infection of the ticks was significantly greater in the urban (46.7%) than in forest habitat (35.4%). Additionally, in the urban site more birds carry at least one infected tick than in the forest. The results of the study seem to confirm the role of blackbirds in establishing Borreliella spp. reservoir. Special regard should be given to highly urbanized areas, where the relative increase in the relevance of birds as tick hosts and pathogen transmitters may pose high risk to public health. Thus, the study constitutes a small-scale but an important contribution to our understanding of the role of birds in maintenance of Borreliella spp. foci in urban habitats.