Chromosome numbers were determined in ten accessions of Phlomis olivieri Benth. (Lamiaceae). The seeds were collected from natural habitats in the west of Iran. Chromosome numbers of all accessions were 2n=2x=20. The chromosomes of accessions were metacentric or submetacentric, ranging in length from 2.66 to 8.604 μm. According to the average values of ten accessions, the karyotype of this species consists of 10 pairs of metacentric chromosomes. An ideogram was depicted for the species. This is the first report on the chromosome number and karyotype analysis of P. olivieri from Iran.