Abstract: The effects of para-phthalic sodium, an organic compound in bauxite, on the sedimentation of red mud was studied, as well as the effects of different concentration of the compound on sedimenting rate, content of overflowing plankton and the ratio of liquid to solid compressed by bottom flow. One of some flocculants was added to eliminate the adverse effect of para-phthalic sodium, and the conditions available to add the flocculant were also studied. The results showed that the concentrations of para-phthalic sodium and flocculant both have important effects on the sedimenting rate of red mud, content of overflowing plankton and the ratio of liquid to solid compressed by bottom flow. Among the 4 flocculants the A-600 is the best one to eliminate the adverse effect of para-phthalic sodium on the sedimenting rate of red mud. If the concentration of para-phthalic sodium is lower than 3.58 g/L, any of the 4 flocculants can eliminate the adverse effect on the compressed liquid/solid ratio of red mud.