Abstract: The karyotype of Thymus mongolicus was analyzed using a chromosome mounting technique. The best sampling time was between 8:45 am and 9:15 am, the best pre-treatment was 0.04% colchicine and 0.002 mol/L 8-hydroxyquinoline mixture (1∶1) for 2-3 h, and the dyeing treatment was 1 h with modified carbolic acid-magenta. Karyotype analysis of T. mongolicus showed that the chromosome number is 24 and the karyotype formula is 2n=2x=24=20m+4sm. Ten pairs are metacentric (m) and 2 pairs are submetacentric (sm). The karyotype of T. mongolicus is 2A and the karyotype asymmetry coefficient is 59.63%.