Karyotyping of Pleurotus eryngii (king oyster mushroom) has been explored by contour-clamped homogeneous electric field (CHEF) gel electrophoresis.Ten chromosomal bands were separated from nuclei of Pleurotus eryngii, this chromosome numbers were confirmed by telomere finger printing.Sizes of the chromosomes were in the range of 3.0 to 7.1 megabase pairs.The total genome size of the strain was estimated to be 43.8Mbp.A certain chromosome was often losted in monokaryotic progenies (basidiospores) and chromosome numbers were varied in the monokaryotic mycelia.