This research was carried out to identify color-causing materials in the coke plant wastewater and to suggest a method to remove color from the coke wastewater treatment plant. For this purpose, coke wastewater treatment process in P company was investigated. The highest difference in color intensity between apparent and true color was observed in ammonia (24%), and the lowest in ammonia washer (7%). Removal efficiency of apparent and true color measured in the secondary clarifier effluent was 38 and 34%, respectively. Color caused by colloidal particles of which size was larger than 0.45 mum and humin was negligible. Maximum and minimum contribution of humic acid in causing F color and other soluble organic materials in causing P color were 23, 24 and 79, 61%, respectively. Maximum and minimum contribution of tannin and lignin in causing P" color were 88 and 79%, respectively. Thus, tannin and lignin are important materials in causing P" color in P" color. Organic materials with molecular weight ranging from 5000 to 1000 were detected in the equalization tank effluent, while those with molecular weight ranging from 2500, 800 and 400 were detected in the secondary clarifier effluent.