In this study, the biodegradability of an untreated and photocatalytically treated solution containing Cibacron Brilliant Yellow 3G-P was examined. Both untreated and partially treated dyes by photocatalysis were used in the biological treatment process. Respirometric measurements indicated that the untreated dye was not inhibitory to biological treatment at the concentration of 100 mg/L. In addition, no significant biodegradation of both untreated and photocatalytically pre-treated dye occurred by either respirometric or conventional BOD tests using activated sludge. Respirometric measurements also suggested that both untreated and treated dye solutions were not biodegradable even with synthetic sewage. Under aerobic condition, partially treated dye solution showed better color removal rate than that of untreated solution. However, biodegradability of the 100 mg/L untreated dye solution was improved by 50% in terms of Oxygen Uptake Rate (OUR) in respirometry by using acclimated sludge.