This study was conducted to investigate the insect community on Rumex obtusifolius L., a naturalized plant in Korea, from October 1998 to September 1999. Five study sites were chosen at Samsan stream near lake Daecheong. Data collection was done onsite every other week during the study period. A total of 5 orders 33 families 85 species was identified. Insects belong to Coleoptera showed highest occurrence in the period from March to May, while insects belong to Hemiptera showed highest occurrence in July. Species diversity of the study area and population dynamics of the selected insects were presented.