Abstract. Paliurus ramosissimus (Rhamnaceae) is a deciduous shrub found on the seashore of Jeju Island, located at the southern tip of the Korean peninsula, and has been designated a rare plant species by the Korea Forest Service. Random amplified polymorphic DNA was used to investigate the genetic variation within and among P. ramosissimus populations on Jeju Island. Populations of P. ramosissimus showed a relatively low genetic diversity. The percentage of polymorphic bands (PPB) ranged from 33.3% to 63.6% (average = 51.4%), Shannon's information index (I) ranged from 0.213 to 0.352 (average = 0.316), and Nei's gene diversity (H) ranged from 0.149 to 0.239 (average = 0.218). Analysis of molecular variance and Nei's gene differentiation coefficient showed low genetic differentiation among populations (Φst = 0.207 and Gst = 0.186). The level of gene flow was sufficient to counter population divergence due to genetic drift (Nm = 0.109). Population genetic information obtained from this study could provide a valuable baseline for conservation and management plans for this species; P. ramosissimus on Jeju Island have to be protected through in situ conservation. The populations Pyo-sun and Il-gwua with high genetic diversity have conservation priority. In particular, Pyo-sun population protection must be the highest priority, as this population was revealed to have a high genetic diversity despite its small size.