The dyeing of cotton fabric with Forsythia koreana NAKAI was investigated. The colorant was extracted with methanol under various concentrations of dyestuffs at 40℃ and 76℃. UV-VIS spectrum was obtained to find the maximum wavelength of colorant. Cotton fabrics were dyed at different temperatures, mordants, in pre and post mordanting methods. The maximum wavelength of spectrum were 390nm, 410nm, 440nm. The highest K/S value was showed at 100% dye concentration, extracted at 76℃ and dyed at 80℃. The mordant effect was not good in the K/S values. The light fastness was increased at Fe-pre mordant and Cr, Fe-post mordant.