Ephemera strigata and E. orientalis are widespread burrowing mayflies in Korea inhabiting sand or fine gravel substrates in lotic habitats. Both of the species have been frequently observed from the same stream region where E. strigata occured in the upper stream areas compared with E. orientalis. This study was conducted to elucidate macro-distributional pattern between the species in relation to altitude. Monthly quantitative field samplings were taken at 12 different sites along alt. 40∼350m in the Sudong Creek in Namyangju, Kyonggi-do, from May to August in 1993. Our results indicated that the distribution of E. strigata ranged alt. 140∼350m(mean 279m, mode 250m) whereas E. orientalis ranged alt. 40∼200m(mean 160m, mode 160) based on total quantitative samplings. A t-test indicated that the distribution between the species was significantly different(p=0.015). Water temperature at study sites was closely correlated with the altitudes. We concluded that the distribution between the species was demarcated at alt. 200∼250m in the Sudong Creek. This attitudinal distribution was similar to the patterns in Japanese Ephemera spp. (E. japonica, E. strigata and E. orientalis). We thus suggest a comparative study of habitat adaptation and evolution between Korean and Japanese Ephemera spp.