We observed the pollen grains and fruits of six Isodon taxa distributed in Korea using a light microscope and a scanning electron microscope. The muri thickness on the surface of the pollen grains distinguishes Isodon serra from other taxa: the thickness of I. serra is ca. 0.6 μm, while the thicknesses of other taxa are 0.37~0.49 μm. I. inflexus var. canescens has a relatively nutlet small (about 0.93×0.83 mm) compared to other Korean Isodon taxa (about 1.15~1.37×1.02~1.17 mm). Characteristically, a nutlet of I. inflexus var. microphyllus has non-glandular hairs distributed all over its surface. However, I. serra has non-glandular hairs distributed only on the top of the nutlet while it has glandular hairs broadly distributed over the entire nutlet. We suggested that these characters of the pollen and fruit surfaces can be included in the key to Korean Isodon as diagnostic characters to distinguish the above taxa from other Korean taxa.