The coagulation performance of cactus to act as natural macromolecular coagulant was studied by the jar test. The cactus coagulation attained comparatively high turbidity removal efficiency, and water with turbidity less than 5NTU could be obtained with initial turbidities from 20 to 200. When used to treat the same water sample, the optimum dosage of cactus coagulant was found similar to that of AlCl3 center dot 6H(2)O. Effects of factors such as pH, temperature, alkalinity on cactus coagulation were also studied. High removal efficiency of turbidity and COD could be obtained when cactus solids were used to treat sewage water, potable water source (taken from Changjiang, Wuhan) and high turbidity seawater. When cactus was used with AlCl3 center dot 6H(2)O synchronously to treat sewage water, the removal efficiency of turbidity and COD were higher than that of cactus or AlCl3 center dot 6H(2)O was used solely. (c) 2005 Elsevier Ltd. All rights reserved.