In recently deglaciated areas, studies of mtDNA haplotype diversity have often revealed clear phylogeographic structure for many animal species. Here, we assessed mitochondrial DNA variation of the moose, Alces alces, in northeastern Poland. Altogether, four haplotypes were found among 45 moose and the haplotype (h) and nucleotide (π) diversity estimates were 0.38 and 0.8%, respectively. The most common haplotype, H1 found in the Biebrza valley, NE Poland was exclusively present in this area and was divergent from the remaining mtDNA haplotypes in the European moose lineage. Our results indicate that the moose population in the Biebrza valley experienced severe bottleneck and could be regarded as a relic group of moose that is very distinct from others in Europe. We also found evidence for population admixture due to immigration, both, in the Biebrza valley and in Poland, in general.