Patterns of epilithic algal colonization on artificial substrata (unglazed ceramic tiles) were investigated from 23rd April to 3rd July 1999 at weekly intervals over a 10 weeks period outside and inside the mesocosm in Togyo reservoir within the Civilian Passage Restriction Line near Demilitarized Zone (DMZ) in Korea. The highest standing crops of epilithic algae was 1,798$cdot$10³ cells$cdot$$cm^{-2}$ outside the mesocosm on 26th June and also inside the mesocosm those was 2,391$cdot$10³ cells$cdot$$cm^{-2}$ on 26th June, 9 weeks after the experiment began. The dominants outside the mesocosm were Achnanthes minutissima, Navicula bicephala, Oscillatoria angusta, Synedra delicastissima, S. tenuissima, S. ulna v. danica and Tabellaria flocculosa, and those inside the mesocosm were Achnanthes minitissima, Coenochloris polycocca, Fragilaria crotonenesis, Peridinium cinctum, Synedra delicatissima, Tabellaria flocculosa and Ulothrix subtilissima. Diatoms were most abundant and Achnanthes minutissima was the most important species colonizing on the tiles. Chlorophyll-a content was highest value of 5.4 mg$cdot$$m^{-2}$ on 19th June after 8 weeks growth outside the mesocosm and was 24.4 mg$cdot$$m^{-2}$ on 26th June, 9 weeks after the experiment began on tiles inside the mesocosm. It was also shown that unglazed ceramic tiles were a more suitable substratum for colonization than the glass slides. Consequently the substratum selection plays an important role in the colonization by the epilithic algal community.