The effects of alkaline magnesium carbonate-hydrated basic as a coagulant, have been investigated in colour reduction experiments using Jar Test apparatus. The raw wastewater was synthetic containing 300 mg/dm3 reactive red dye 519. It has been found that no single flocculant (Mg(OH)2, Ca(OH)2 or CaCO3) can satisfactorily effect colour removal. The effective colour reduction achieved using alkaline magnesium carbonate-hydrated basic has been attributed to the synergistic sorbing capacity of the flocculants Mg(OH)2 and CaCO3.