Constitutive heterochromatin in higher eukaryotes is located in the primary chromosomal strangulation (centromeres and pericentromeres) and subtelomeric regions of chromosomes. In house mouse constitutive chromatin formes structures in the nuclei of cells, brightly colored with DAPI. It is known that the constitutive heterochromatin is enriched with large tandem repeats, however, its exact composition is unknown. In this paper chromocenters were studied using several approaches: cloning and sequencing by Sanger, as well as by high-throughput sequencing. We have shown that DNA components of chromocenters and constitutive chromatin are full-length endogenous retroviruses (ERV) and a 2 kbp fragment of the 3R-end of the LINE.